Editorial: Dry electroencephalography for brain monitoring in sports and movement science. - In: Frontiers in neuroscience, ISSN 1662-453X, Bd. 15 (2021), 809227, S. 1-2
https://doi.org/10.3389/fnins.2021.809227
Boundary element fast multipole method for modeling electrical brain stimulation with voltage and current electrodes. - In: Journal of neural engineering, ISSN 1741-2552, Bd. 18 (2021), 4, 0460d4, S. 1-21
Objective. To formulate, validate, and apply an alternative to the finite element method (FEM) high-resolution modeling technique for electrical brain stimulation - the boundary element fast multipole method (BEM-FMM). To include practical electrode models for both surface and embedded electrodes. Approach. Integral equations of the boundary element method in terms of surface charge density are combined with a general-purpose fast multipole method and are expanded for voltage, shunt, current, and floating electrodes. The solution of coupled and properly weighted/preconditioned integral equations is accompanied by enforcing global conservation laws: charge conservation law and Kirchhoff's current law. Main results. A sub-percent accuracy is reported as compared to the analytical solutions and simple validation geometries. Comparison to FEM considering realistic head models resulted in relative differences of the electric field magnitude in the range of 3%-6% or less. Quantities that contain higher order spatial derivatives, such as the activating function, are determined with a higher accuracy and a faster speed as compared to the FEM. The method can be easily combined with existing head modeling pipelines such as headreco or mri2mesh. Significance. The BEM-FMM does not rely on a volumetric mesh and is therefore particularly suitable for modeling some mesoscale problems with submillimeter (and possibly finer) resolution with high accuracy at moderate computational cost. Utilizing Helmholtz reciprocity principle makes it possible to expand the method to a solution of EEG forward problems with a very large number of cortical dipoles.
https://doi.org/10.1088/1741-2552/ac17d7
Magnetic field compensation coil design for magnetoencephalography. - In: Scientific reports, ISSN 2045-2322, Bd. 11 (2021), 22650, S. 1-12
While optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately 5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.
https://doi.org/10.1038/s41598-021-01894-z
Fortschritte in der Entwicklung einer Planck-Waage (Planck-Balance 2 - PB2): eine Tabletop-Kibble-Waage zur Kalibrierung von Gewichten der Klasse E2 :
The progress in development of the Planck-Balance 2 (PB2): a tabletop Kibble balance for the mass calibration of E2 class weights. - In: Technisches Messen, ISSN 2196-7113, Bd. 88 (2021), 12, S. 731-756
In this paper we present the progress in development of a table-top version of the Kibble balance under the name Planck-Balance 2 (PB2). The PB2 is developed as a collaboration effort between the Technische Universität Ilmenau (TU Ilmenau) and Physikalisch-Technische Bundesanstalt (PTB) aiming for automatized mass calibration of the set of weights in the range from 1 mg to 100 g within the required uncertainties as stated by OIML recommendation R111 for weights of E2 class. We describe the design and the operational performance of the PB2 system in detail, the results of rigorous investigations of the error sources and subsequent improvements made since the beginning of the project in early 2017, the measurement data with the corresponding relative uncertainties and the preliminarily obtained uncertainty budget.
https://doi.org/10.1515/teme-2021-0101
Fibre-optical calibration of position sensors for Planck-Balances :
Faseroptische Kalibrierung von Positionssensoren für Planck-Waagen. - In: Technisches Messen, ISSN 2196-7113, Bd. 88 (2021), 12, S. 757-763
Zur Kibble-Kalibrierung von EMK-Systemen (sogenannte Planck-Waagen) muss die induzierte Spulenspannung, sowie die Geschwindigkeit der Aktorspule während der Bewegung relativ zum Magnetfeld erfasst werden. Die Bestimmung der Geschwindigkeit erfolgt anhand der, über die Zeit, gemessenen Position. Als Alternative zur interferometrischen Messung wird in diesem Artikel ein Verfahren zur faseroptischen Kalibrierung der, bei EMK-Systemen weit verbreiteten, optischen Positionssensoren vorgestellt. Der eigens entwickelte faseroptische Sensor, sowie die theoretisch beschriebene Kalibrierung wurden an einer Planck-Waage messtechnisch validiert. Im direkten Vergleich mit einem kommerziellen Interferometer wurden Kennlinienabweichungen von unter 60 nm über einem Bewegungsbereich von ± 12 [my]m erzielt.
https://doi.org/10.1515/teme-2021-0106
Quantum-based sensors for detection and discretization of currents in EMFC weighing systems :
Quantenbasierte Sensorik zur Erfassung und Diskretisierung von Strömen für EMK-Wägesysteme. - In: Technisches Messen, ISSN 2196-7113, Bd. 88 (2021), 12, S. 764-772
Hochpräzise Wägesysteme nach dem Prinzip der elektromagnetischen Kraftkompensation (EMK), wie Massekomparatoren, finden trotz Neudefinition der Einheit Kilogramm weiterhin Anwendung bei der Realisierung sowie Weitergabe einer praktischen Masseskale, indem sie metrologische Massevergleiche anhand des elektrischen Stromes als Zwischengröße ermöglichen. Gleichzeitig haben Quanteninterferometer auf Basis einer supraleitenden Hochgeschwindigkeitselektronik das Potential, kleinste Änderungen des magnetischen Flusses im Femtotesla-Bereich aufzulösen und eröffnen somit einen alternativen Ansatz zum Erfassen kleinster Stromdifferenzen. Die Kombination dieser bislang größtenteils nur für Fundamentalexperimente in der elektrischen Metrologie ausgenutzten quantenelektrischen Effekte mit Systemen der Präzisionskraftmessung ist eine neuartige Ausgangsbasis zur Verbesserung der Messgenauigkeit dieser Referenzsysteme. Insbesondere bietet die Anwendung eines quantenbasierten Analog-zu-Digital-Wandlers ein deutliches Potential zum Erschließen bisher unerreichter Genauigkeiten. In diesem Beitrag werden die Ergebnisse erster experimenteller Arbeiten zum Nachweis des grundlegenden Funktionsprinzips präsentiert. Darüber hinaus erfolgt eine Abschätzung der Leistungsfähigkeit sowie des Entwicklungspotentials des vorgestellten quantenbasierten Stromsensors für hochpräzise EMK-Wägesysteme.
https://doi.org/10.1515/teme-2021-0089
Freeform direct laser writing of versatile topological 3D scaffolds enabled by intrinsic support hydrogel. - In: Materials Horizons, ISSN 2051-6355, Bd. 8 (2021), 12, S. 3334-3344
In this study, a novel approach to create arbitrarily shaped 3D hydrogel objects is presented, wherein freeform two-photon polymerization (2PP) is enabled by the combination of a photosensitive hydrogel and an intrinsic support matrix. This way, topologies without physical contact such as a highly porous 3D network of concatenated rings were realized, which are impossible to manufacture with most current 3D printing technologies. Micro-Raman and nanoindentation measurements show the possibility to control water uptake and hence tailor the Young's modulus of the structures via the light dosage, proving the versatility of the concept regarding many scaffold characteristics that makes it well suited for cell specific cell culture as demonstrated by cultivation of human induced pluripotent stem cell derived cardiomyocytes.
https://doi.org/10.1039/D1MH00925G
Reservoir computing with delayed input for fast and easy optimisation. - In: Entropy, ISSN 1099-4300, Bd. 23 (2021), 12, 1560, S. 1-13
Reservoir computing is a machine learning method that solves tasks using the response of a dynamical system to a certain input. As the training scheme only involves optimising the weights of the responses of the dynamical system, this method is particularly suited for hardware implementation. Furthermore, the inherent memory of dynamical systems which are suitable for use as reservoirs mean that this method has the potential to perform well on time series prediction tasks, as well as other tasks with time dependence. However, reservoir computing still requires extensive task-dependent parameter optimisation in order to achieve good performance. We demonstrate that by including a time-delayed version of the input for various time series prediction tasks, good performance can be achieved with an unoptimised reservoir. Furthermore, we show that by including the appropriate time-delayed input, one unaltered reservoir can perform well on six different time series prediction tasks at a very low computational expense. Our approach is of particular relevance to hardware implemented reservoirs, as one does not necessarily have access to pertinent optimisation parameters in physical systems but the inclusion of an additional input is generally possible.
https://doi.org/10.3390/e23121560
Gaining insight into the deformation of Achilles tendon entheses in mice. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 23 (2021), 11, 2100085, S. 1-11
Understanding the biomechanics of tendon entheses is fundamental for surgical repair and tissue engineering but also relevant in biomimetics and paleontology. Examinations into the 3D tissue deformation under load are an important element in this process. However, entheses are difficult objects for microcomputed tomography due to extreme differences in X-ray attenuation. Herein, the ex vivo examination of Achilles tendon entheses from mice using a combination of tensile tests and synchrotron radiation-based microcomputed tomography is reported. Strains and volume changes are compared between the more proximal free tendon and the distal tendon that wraps around the Tuber calcanei. Tomographic datasets of relaxed and deformed entheses are recorded with propagation-based phase contrast. The tissue structure is rendered in sufficient detail to enable manual tracking of patterns along the tendon, as well as digital volume correlation in a suitable pair of tomographic datasets. The strains are higher in the distal than in the proximal tendon. These results support the existence of a compliant zone near the insertion. Necessary steps to extend the automatic tracking of tissue displacements to all stages of the deformation experiment are discussed.
https://doi.org/10.1002/adem.202100085
Dialysis diffusion kinetics in polymer purification. - In: Macromolecules, ISSN 1520-5835, Bd. 54 (2021), 20, S. 9410-9417
Diffusion kinetics of a prior developed automated dialysis system are investigated via in situ NMR spectroscopy for an optimization of conventional and advanced polymer purification. Using a polymeric solution, mixed with the respective monomer, several parameters like starting concentration, solvent volume, and solvent exchange by flow or complete one-time exchange are varied, resulting in a significant decrease of purification time for the automated setup. With an increased solvent flow (from 0.9 to 5.5 mL/min), 5.4 h and 2000 mL of solvent are required to decrease the monomer concentration to the detection limit. Without solvent flow, which corresponds to conventional dialysis, only 9 h and 250 mL of solvent are required for the same result, which is a time- and solvent-saving development for common purification of polymers.
https://doi.org/10.1021/acs.macromol.1c01241