Electric field temporal interference stimulation of neurons in vitro. - In: Lab on a chip, ISSN 1473-0189, Bd. 0 (2024), 0, insges. 13 S.
Electrical stimulation (ES) techniques, such as deep brain and transcranial electrical stimulation, have shown promise in alleviating the symptoms of depression and other neurological disorders in vivo. A new noninvasive ES method called temporal interference stimulation (TIS), possesses great potential as it can be used to steer the stimulation and possibly selectively modulate different brain regions. To study TIS in a controlled environment, we successfully established an in vitro ‘TIS on a chip’ setup using rat cortical neurons on microelectrode arrays (MEAs) in combination with a current stimulator. We validated the developed TIS system and demonstrated the spatial steerability of the stimulation by direct electric field measurements in the chip setup. We stimulated cultures of rat cortical neurons at 28 days in vitro (DIV) by two-channel stimulation delivering 1) TIS at 653 Hz and 643 Hz, resulting in a 10 Hz frequency envelope, 2) low-frequency stimulation (LFS) at 10 Hz and 3) high-frequency stimulation (HFS) at 653 Hz. Unstimulated cultures were used as control/sham. We observed the differences in the electric field strengths during TIS, HFS, and LFS. Moreover, HFS and LFS had the smallest effects on neuronal activity. Instead, TIS elicited neuronal electrophysiological responses, especially 24 hours after stimulation. Our ‘TIS on a chip’ approach eludicates the applicability of TIS as a method to modulate neuronal electrophysiological activity. The TIS on a chip approach provides spatially steerable stimuli while mitigating the effects of high stimulus fields near the stimulation electrodes. Thus, the approach opens new avenues for stimulation on a chip applications, allowing the study of neuronal responses to gain insights into the potential clinical applications of TIS in treating various brain disorders.
https://doi.org/10.1039/D4LC00224E
Elucidating the transport of electrons and molecules in a solid electrolyte interphase close to battery operation potentials using a four-electrode-based generator-collector setup. - In: Journal of the American Chemical Society, ISSN 1520-5126, Bd. 146 (2024), 28, S. 19009-19018
In lithium-ion batteries, the solid electrolyte interphase (SEI) passivates the anode against reductive decomposition of the electrolyte but allows for electron transfer reactions between anode and redox shuttle molecules, which are added to the electrolyte as an internal overcharge protection. In order to elucidate the origin of these poorly understood passivation properties of the SEI with regard to different molecules, we used a four-electrode-based generator-collector setup to distinguish between electrolyte reduction current and the redox molecule (ferrocenium ion Fc+) reduction current at an SEI-covered glassy carbon electrode. The experiments were carried out in situ during potentiostatic SEI formation close to battery operation potentials. The measured generator and collector currents were used to calculate passivation factors of the SEI with regard to electrolyte reduction and with regard to Fc+ reduction. These passivation factors show huge differences in their absolute values and in their temporal evolution. By making simple assumptions about molecule transport, electron transport, and charge transfer reaction rates in the SEI, distinct passivation mechanisms are identified, strong indication is found for a transition during SEI growth from redox molecule reduction at the electrode | SEI interface to reduction at the SEI | electrolyte interface, and good estimates for the transport coefficients of both electrons and redox molecules are derived. The approach presented here is applicable to any type of electrochemical interphase and should thus also be of interest for interphase characterization in the fields of electrocatalysis and corrosion.
https://doi.org/10.1021/jacs.4c03029
Uncertainty of a calibration device for heat flux sensors - uncertainty of the temperature difference :
Messunsicherheit einer Kalibriereinrichtung für Wärmestromsensoren - Unsicherheit der Temperaturdifferenz. - In: Technisches Messen, ISSN 2196-7113, Bd. 0 (2024), 0, S. 1-10
Wärmestromsensoren werden in den verschiedensten Applikationen eingesetzt. Dabei ist eine Kalibrierung der Sensoren unumgänglich. In diesem Beitrag wird die Bedeutung von Wärmestromsensoren und die Notwendigkeit einer Kalibrierung aufgezeigt. Zu diesem Zweck wurde am Institut für Prozessmess- und Sensortechnik der Technischen Universität Ilmenau ein Kalibrierstand entwickelt und aufgebaut, der die rückführbare Kalibrierung von Wärmestromsensoren ermöglicht. Mit dieser Einrichtung können Wärmestromsensoren durch einen Vergleich gegenüber einem Referenzwärmestromsensor, basierend auf Wärmeleitprozessen, kalibriert werden. Vor diesem Hintergrund wird der Aufbau der Kalibriereinrichtung sowie der enthaltenen Sensorik diskutiert und eine umfassende Unsicherheitsbetrachtung zum eingeprägten Wärmestrom angestellt. Der Schwerpunkt dieser Unsicherheitsbetrachtung liegt auf der Messung von Temperaturdifferenzen innerhalb der Einrichtung, die einen maßgeblichen Einfluss auf die Unsicherheit des rückführbaren Wärmestroms haben. Aus der umfassenden Unsicherheitsbetrachtung resultiert für den bereitgestellten Wärmestrom in der Kalibriereinrichtung eine um ( k = 2) erweiterte relative Messunsicherheit von 2,9%.
https://doi.org/10.1515/teme-2024-0034
Flexures for Kibble balances: minimizing the effects of anelastic relaxation. - In: Metrologia, ISSN 1681-7575, Bd. 61 (2024), 4, 045006, S. 1-18
We studied the anelastic aftereffect of a flexure being used in a Kibble balance, where the flexure is subjected to a large excursion in velocity mode after which a high-precision force comparison is performed. We investigated the effect of a constant and a sinusoidal excursion on the force comparison. We explored theoretically and experimentally a simple erasing procedure, i.e. bending the flexure in the opposite direction for a given amplitude and time. We found that the erasing procedure reduced the time-dependent force by about 30%. The investigation was performed with an analytical model and verified experimentally with our new Kibble balance at the National Institute of Standards and Technology employing flexures made from precipitation-hardened Copper Beryllium alloy C17200. Our experimental determination of the modulus defect of the flexure yields 1.2 x 10^-4. This result is about a factor of two higher than previously reported from experiments. We additionally found a static shift of the flexure’s internal equilibrium after a change in the stress and strain state. These static shifts, although measurable, are small and deemed uncritical for our Kibble balance application at present. During this investigation, we discovered magic flexures that promise to have very little anelastic relaxation. In these magic flexures, the mechanism causing anelastic relaxation is compensated for by properly shaping and loading a flexure with a non-constant cross-section in the region of bending.
https://doi.org/10.1088/1681-7575/ad57cb
A novel magnet system - which enables uniformity of radial flux density by means of a parabolic yoke - applied in the Planck-Balance. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 10, 105004, S. 1-9
A uniform magnetic flux density that is effective in the movement range of the coil is essential for accurate Kibble balance experiments. By utilizing Hopkinson’s law and Kirchhoff’s circuit laws, basic formulas have been derived, providing a method to calculate the magnetic flux density distribution in the airgap of a cylindrical magnet system. A parabolic outer contour of the inner yoke has been found to be a suitable solution to achieve uniformity. Experiments show, that this approach results in a relative change of magnetic flux density in the order of 3 &hahog; 10^-4 per 8 mm movement range, using a magnet system with a mass of only 2.3 kg. Therefore, the system will be integrated into the upgraded version of PTB’s Planck-Balance - a compact variant of a Kibble balance - aiming for sub 1 &hahog; 10^-6 accuracy level determination of the geometric factor. The solution described provides a comparatively easy means to design a cylindrical magnet system, using only one permanent magnet disc, without the use of complex simulation software.
https://doi.org/10.1088/1361-6501/ad52b6
On the prediction of the turbulent flow behind cylinder arrays via echo state networks. - In: Machine learning: science and technology, ISSN 2632-2153, Bd. 5 (2024), 3, 035005, S. 1-18
This study aims at the prediction of the turbulent flow behind cylinder arrays by the application of Echo State Networks (ESN). Three different arrangements of arrays of seven cylinders are chosen for the current study. These represent different flow regimes: single bluff body flow, transient flow, and co-shedding flow. This allows the investigation of turbulent flows that fundamentally originate from wake flows yet exhibit highly diverse dynamics. The data is reduced by Proper Orthogonal Decomposition (POD) which is optimal in terms of kinetic energy. The Time Coefficients of the POD Modes (TCPM) are predicted by the ESN. The network architecture is optimized with respect to its three main hyperparameters, Input Scaling (INS), Spectral Radius (SR), and Leaking Rate (LR), in order to produce the best predictions in terms of Weighted Prediction Score (WPS), a metric leveling statistic and deterministic prediction. In general, the ESN is capable of imitating the complex dynamics of turbulent flows even for longer periods of several vortex shedding cycles. Furthermore, the mutual interdependencies of the TCPM are well preserved. However, optimal hyperparameters depend strongly on the flow characteristics. Generally, as flow dynamics become faster and more intermittent, larger LR and INS values result in better predictions, whereas less clear trends for SR are observable.
https://doi.org/10.1088/2632-2153/ad5414
Delivery of TGFβ3 from magnetically responsive coaxial fibers reduces spinal cord astrocyte reactivity in vitro. - In: Advanced biology, ISSN 2701-0198, Bd. 0 (2024), 0, 2300531, S. 1-14
A spinal cord injury (SCI) compresses the spinal cord, killing neurons and glia at the injury site and resulting in prolonged inflammation and scarring that prevents regeneration. Astrocytes, the main glia in the spinal cord, become reactive following SCI and contribute to adverse outcomes. The anti-inflammatory cytokine transforming growth factor beta 3 (TGFβ3) has been shown to mitigate astrocyte reactivity; however, the effects of prolonged TGFβ3 exposure on reactive astrocyte phenotype have not yet been explored. This study investigates whether magnetic core-shell electrospun fibers can be used to alter the release rate of TGFβ3 using externally applied magnetic fields, with the eventual application of tailored drug delivery based on SCI severity. Magnetic core-shell fibers are fabricated by incorporating superparamagnetic iron oxide nanoparticles (SPIONs) into the shell and TGFβ3 into the core solution for coaxial electrospinning. Magnetic field stimulation increased the release rate of TGFβ3 from the fibers by 25% over 7 days and released TGFβ3 reduced gene expression of key astrocyte reactivity markers by at least twofold. This is the first study to magnetically deliver bioactive proteins from magnetic fibers and to assess the effect of sustained release of TGFβ3 on reactive astrocyte phenotype.
https://doi.org/10.1002/adbi.202300531
Simulation of heat transfer and propagation velocity for different heat loss conditions for guided propagation fronts in reactive multilayer foils. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2400523, S. 1-9
Engineering self-propagating reactions in reactive material systems requires an understanding of critical ignition and propagation conditions. These conditions are governed by the material properties of the reactive materials responsible for net heat generation, as well as by external environmental conditions that primarily determine net heat loss. In this study, it is aimed to utilize a numerical model to investigate the critical conditions for reaction propagation based solely on the heat-transfer equation, enabling thorough examination with significantly low computational effort. Comparing simulations with experiments demonstrates a high level of agreement in predicting reaction propagation. Additionally, this numerical model provides valuable information regarding heat distribution in substrate materials.
https://doi.org/10.1002/adem.202400523
Magnetic barium hexaferrite nanoparticles with tunable coercivity as potential magnetic heating agents. - In: Nanomaterials, ISSN 2079-4991, Bd. 14 (2024), 12, 992, S. 1-20
Using magnetic nanoparticles (MNPs) for extracorporeal heating applications results in higher field strength and, therefore, particles of higher coercivity can be used, compared to intracorporeal applications. In this study, we report the synthesis and characterization of barium hexa-ferrite (BaFe12O19) nanoparticles as potential particles for magnetic heating. Using a precipitation method followed by high-temperature calcination, we first studied the influence of varied synthesis parameters on the particles’ properties. Second, the iron-to-barium ratio (Fe/Ba = r) was varied between 2 and 12. Vibrating sample magnetometry, scanning electron microscopy and X-ray diffraction were used for characterization. A considerable influence of the calcination temperature (Tcal) was found on the resulting magnetic properties, with a decrease in coercivity (HC) from values above 370 kA/m for Tcal = 800-1000 ˚C to HC = 45-70 kA/m for Tcal = 1200 ˚C. We attribute this drop in HC mainly to the formation of entirely multi-domain particles at high Tcal. For the varying Fe/Ba ratios, increasing amounts of BaFe2O4 as an additional phase were detected by XRD in the small r (barium surplus) samples, lowering the particles’ magnetization. A decrease in HC was found in the increased r samples. Crystal size ranged from 47 nm to 240 nm and large agglomerates were seen in SEM images. The reported particles, due to their controllable coercivity, can be a candidate for extracorporeal heating applications in the biomedical or biotechnological field.
https://doi.org/10.3390/nano14120992
A new stress tensor approach for application to the conductor surface. - In: Compel, ISSN 2054-5606, Bd. 0 (2024), 0
Purpose: The purpose of this paper is to derive a new stress tensor for calculating the Lorentz force acting on an arbitrarily shaped nonmagnetic conductive specimen moving in the field of a permanent magnet. The stress tensor allows for a transition from a volume to a surface integral for force calculation. Design/methodology/approach: This paper derives a new stress tensor which consists of two parts: the first part corresponds to the scaled Poynting vector and the second part corresponds to the velocity term. This paper converts the triple integral over the volume of the conductor to a double integral over its surface, where the subintegral functions are continuous through the different compartments of the model. Numerical results and comparison to the standard volume discretization using the finite element method are given. Findings: This paper evaluated the performance of the new stress tensor computation on a thick and thin cuboid, a thin disk, a sphere and a thin cuboid containing a surface defect. The integrals are valid for any geometry of the specimen and the position and orientation of the magnet. The normalized root mean square errors are below 0.26% with respect to a reference finite element solution applying volume integration. Originality/value: Tensor elements are continuous throughout the model, allowing integration directly over the conductor surface.
https://doi.org/10.1108/COMPEL-10-2023-0543