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- ItemComplement activation by carbon nanotubes and its influence on the phagocytosis and cytokine response by macrophages(Amsterdam [u.a.] : Elsevier, 2014) Pondman, K.M.; Sobik, M.; Nayak, A.; Tsolaki, A.G.; Jäkel, A.; Flahaut, E.; Hampel, S.; ten Haken, B.; Sim, R.B.; Kishore, U.Carbon nanotubes (CNTs) have promised a range of applications in biomedicine. Although influenced by the dispersants used, CNTs are recognized by the innate immune system, predominantly by the classical pathway of the complement system. Here, we confirm that complement activation by the CNT used continues up to C3 and C5, indicating that the entire complement system is activated including the formation of membrane-attack complexes. Using recombinant forms of the globular regions of human C1q (gC1q) as inhibitors of CNT-mediated classical pathway activation, we show that C1q, the first recognition subcomponent of the classical pathway, binds CNTs via the gC1q domain. Complement opsonisation of CNTs significantly enhances their uptake by U937 cells, with concomitant downregulation of pro-inflammatory cytokines and up-regulation of anti-inflammatory cytokines in both U937 cells and human monocytes. We propose that CNT-mediated complement activation may cause recruitment of cellular infiltration, followed by phagocytosis without inducing a pro-inflammatory immune response. From the Clinical Editor: This study highlights the importance of the complement system in response to carbon nanontube administration, suggesting that the ensuing complement activation may cause recruitment of cellular infiltration, followed by phagocytosis without inducing a pro-inflammatory immune response.
- ItemThe complexity of surface acoustic wave fields used for microfluidic applications(Amsterdam [u.a.] : Elsevier, 2020) Weser, R.; Winkler, A.; Weihnacht, M.; Menzel, S.; Schmidt, H.Using surface acoustic waves (SAW) for the agitation and manipulation of fluids and immersed particles or cells in lab-on-a-chip systems has been state of the art for several years. Basic tasks comprise fluid mixing, atomization of liquids as well as sorting and separation (or trapping) of particles and cells, e.g. in so-called acoustic tweezers. Even though the fundamental principles governing SAW excitation and propagation on anisotropic, piezoelectric substrates are well-investigated, the complexity of wave field effects including SAW diffraction, refraction and interference cannot be comprehensively simulated at this point of time with sufficient accuracy. However, the design of microfluidic actuators relies on a profound knowledge of SAW propagation, including superposition of multiple SAWs, to achieve the predestined functionality of the devices. Here, we present extensive experimental results of high-resolution analysis of the lateral distribution of the complex displacement amplitude, i.e. the wave field, alongside with the electrical S-parameters of the generating transducers. These measurements were carried out and are compared in setups utilizing travelling SAW (tSAW) excited by single interdigital transducer (IDT), standing SAW generated between two IDTs (1DsSAW, 1D acoustic tweezers) and between two pairs of IDTs (2DsSAW, 2D acoustic tweezers) with different angular alignment in respect to pure Rayleigh mode propagation directions and other practically relevant orientations. For these basic configurations, typically used to drive SAW-based microfluidics, the influence of common SAW phenomena including beam steering, coupling coefficient dispersion and diffraction on the resultant wave field is investigated. The results show how tailoring of the acoustic conditions, based on profound knowledge of the physical effects, can be achieved to finally realize a desired behavior of a SAW-based microacoustic-fluidic system. © 2020 Elsevier B.V.
- ItemPulsed-field Invasion to HTS Bulk Magnets Grown from Two Seeds with Varied Seed-crystal Positions and Numbers(Amsterdam [u.a.] : Elsevier, 2014) Oka, T.; Yamada, Y.; Horiuchi, T.; Ogawa, J.; Fukui, S.; Sato, T.; Yokoyama, K.; Langer, M.The flux-invasion behavior into the melt-processed Y-Ba-Cu-O bulk magnets were precisely measured and analyzed during and after their pulsed-field magnetization processes operated at 30.6 K. The materials were fabricated as the bulk monoliths grown by adopting two seed-crystals, or shifting the seed-crystal positions from the centre of the sample surface, which exhibited the magnetically single-domain distributions. Although the performances of the trapped flux density after activations showed no obvious differences, the flux started invading into the sample bearing two seeds obviously at lower fields than those of normally-grown isotropic crystal. Since the flux penetration behavior were thus clearly different between the samples with the structure grown from two seeds and uniformly grown samples with a seed crystal, it is suggested that the structure results in an effective magnetizing method with less heating than those of conventional samples, which results in the higher performance of field trapping in the bulk magnets than usual.
- ItemMeasurements of Streams Agitated by Fluid Loaded SAW-devices Using a Volumetric 3-component Measurement Technique (V3V)(Amsterdam [u.a.] : Elsevier, 2015) Kiebert, Florian; König, Jörg; Kykal, Carsten; Schmidt, HagenUtilizing surface acoustic waves (SAW) to induce tailored fluid motion via the acoustic streaming requires detailed knowledge about the acoustic bulk wave excitation. For the first time, the Defocus Digital Particle Image Velocimetry is used to measure the fluid motion originating from a fluid loaded SAW-device. With this flow measurement technique, the acoustic streaming-induced fluid motion can be observed volumetrically, which is attractive not only for application, but also for simulation in order to gain deeper insights regarding three-dimensional acoustic effects.
- ItemAutomated meshing of electron backscatter diffraction data and application to finite element micromagnetics(Amsterdam [u.a.] : Elsevier, 2019) Gusenbauer, Markus; Fischbacher, Johann; Kovacs, Alexander; Oezelt, Harald; Bance, Simon; Zhao, Panpan; Woodcock, Thomas George; Schrefl, ThomasThis paper gives a procedure for automatically generating finite element meshes with an adaptive mesh size from Electron Backscatter Diffraction (EBSD) data. After describing the procedure in detail, including preliminary and image processing steps, an example application is given. The method was used to carry out finite element (FE) micromagnetic simulations based on real microstructures in the hard magnetic material, MnAl. A fast micromagnetic solver was used to compute hysteresis properties from the finite element mesh generated automatically from EBSD data. The visualization of the magnetization evolution showed that the reversal is governed by domain wall pinning at twin boundaries. The calculated coercive fields are very sensitive to changes of the Gilbert damping constant, even for low field rates. © 2019 The Authors
- ItemAcoustic resonance effects and cavitation in SAW aerosol generation(Amsterdam [u.a.] : Elsevier, 2023) Roudini, Mehrzad; Manuel Rosselló, Juan; Manor, Ofer; Ohl, Claus-Dieter; Winkler, AndreasThe interaction of surface acoustic waves (SAWs) with liquids enables the production of aerosols with adjustable droplet sizes in the micrometer range expelled from a very compact source. Understanding the nonlinear acousto-hydrodynamics of SAWs with a regulated micro-scale liquid film is essential for acousto-microfluidics platforms, particularly aerosol generators. In this study, we demonstrate the presence of micro-cavitation in a MHz-frequency SAW aerosol generation platform, which is touted as a leap in aerosol technology with versatile application fields including biomolecule inhalation therapy, micro-chromatography and spectroscopy, olfactory displays, and material deposition. Using analysis methods with high temporal and spatial resolution, we demonstrate that SAWs stabilize spatially arranged liquid micro-domes atop the generator's surface. Our experiments show that these liquid domes become acoustic resonators with highly fluctuating pressure amplitudes that can even nucleate cavitation bubbles, as supported by analytical modeling. The observed fragmentation of liquid domes indicates the participation of three droplet generation mechanisms, including cavitation and capillary-wave instabilities. During aerosol generation, the cavitation bubbles contribute to the ejection of droplets from the liquid domes and also explain observed microstructural damage patterns on the chip surface eventually caused by cavitation-based erosion.
- ItemProcessing metallic glasses by selective laser melting(Amsterdam [u.a.] : Elsevier, 2013) Pauly, S.; Löber, L.; Petters, R.; Stoica, M.; Scudino, S.; Kühn, U.; Eckert, J.Metallic glasses and their descendants, the so-called bulk metallic glasses (BMGs), can be regarded as frozen liquids with a high resistance to crystallization. The lack of a conventional structure turns them into a material exhibiting near-theoretical strength, low Young's modulus and large elasticity. These unique mechanical properties can be only obtained when the metallic melts are rapidly cooled to bypass the nucleation and growth of crystals. Most of the commonly known and used processing routes, such as casting, melt spinning or gas atomization, have intrinsic limitations regarding the complexity and dimensions of the geometries. Here, it is shown that selective laser melting (SLM), which is usually used to process conventional metallic alloys and polymers, can be applied to implement complex geometries and components from an Fe-base metallic glass. This approach is in principle viable for a large variety of metallic alloys and paves the way for the novel synthesis of materials and the development of parts with advanced functional and structural properties without limitations in size and intricacy.
- ItemAb initio based study of finite-temperature structural, elastic and thermodynamic properties of FeTi(Amsterdam [u.a.] : Elsevier, 2014) Zhu, L.-F.; Friák, M.; Udyansky, A.; Ma, D.; Schlieter, A.; Kühn, U.; Eckert, J.; Neugebauer, J.We employ density functional theory (DFT) to calculate pressure dependences of selected thermodynamic, structural and elastic properties as well as electronic structure characteristics of equiatomic B2 FeTi. We predict ground-state single-crystalline Young's modulus and its two-dimensional counterpart, the area modulus, together with homogenized polycrystalline elastic parameters. Regarding the electronic structure of FeTi, we analyze the band structure and electronic density of states. Employing (i) an analytical dynamical matrix parametrized in terms of elastic constants and lattice parameters in combination with (ii) the quasiharmonic approximation we then obtained free energies, the thermal expansion coefficient, heat capacities at constant pressure and volume, as well as isothermal bulk moduli at finite temperatures. Experimental measurements of thermal expansion coefficient complement our theoretical investigation and confirm our theoretical predictions. It is worth mentioning that, as often detected in other intermetallics, some materials properties of FeTi strongly differ from the average of the corresponding values found in elemental Fe and Ti. These findings can have important implications for future materials design of new intermetallic materials.
- ItemAdvanced thermal stability investigations of the Mn–Al-Ga system(Amsterdam [u.a.] : Elsevier, 2020) Mix, T.; Woodcock, T.G.A ternary Mn–Al-Ga alloy with the nominal composition Mn55Al38.57Ga6.43 was produced by arc melting. After homogenisation, the alloy consisted of the ε and γ2 phases. Appropriate heat treatments were used to transform each of these into a phase with the L10 structure. These two L10 phases had different compositions, lattice parameters and magnetic properties. In order to test the stability of the L10 phases against decomposition, heat treatments were carried out at 700 °C for durations of up to 14 days. The results showed that the decomposition started with formation of the β-Mn phase and subsequent appearance of the γ2 phase. The resulting diffusion gradients resulted in composition changes in the L10 phases and after 7 days, only a single, intermediate composition remained. After 14 days, the decomposition was almost complete. The decomposition of the L10 phases in the ternary Mn–Al-Ga alloy was significantly slower than in binary Mn–Al alloys.
- ItemNaOH protective layer for a stable sodium metal anode in liquid electrolytes(Amsterdam [u.a.] : Elsevier, 2024) Thomas, Alexander; Pohle, Björn; Schultz, Johannes; Hantusch, Martin; Mikhailova, DariaSodium is known as a soft metal that can easily change its particle morphology. It can form outstretched and rolled fibers with plastic or brittle behavior, and cubes. In Na-batteries, metallic Na anodes demonstrate a high reactivity towards the majority of electrolyte solutions, volume change and a random deposition process from the electrolyte, accompanied by dendrite formation. In order to smooth the electrochemical Na deposition, we propose NaOH as a simple artificial protective layer for sodium, formed by its exposure to ambient conditions for a certain period of time. The formed NaOH layer on top of the metallic sodium suppresses the volume change and dendrite growth on the sodium surface. Additionally, the protected sodium does not change its morphology after a prolonged contact with carbonate-based electrolytes. In symmetric Na-batteries, the NaOH layer increases the lifetime of the electrochemical cell by eight times in comparison to non-protected Na. In the full-cell with a layered sodium oxide cathode, the NaOH-protected sodium anode also leads to a high cycling stability, providing 81 % of the initial cell capacity after 500 cycles with a 1C current rate. In contrast, batteries with a non-protected Na-anode reach only 20 % of their initial capacity under the same conditions. Therefore, the main benefits of the NaOH artificial layer are the chemical compatibility with the carbonate-based electrolytes, the protection of Na metal against reaction with the electrolyte solution, the rapid Na-ion diffusion through the layer and the formation of a mechanical barrier, mitigating Na-dendrite growth. This work presents an easily scalable method to protect sodium without any additional chemicals or a special environment for this reaction.