Combined particle image velocimetry and thermometry of turbulent superstructures in thermal convection. - In: Journal of fluid mechanics, ISSN 1469-7645, Bd. 945 (2022), A22, S. A22-1-A22-25
Turbulent superstructures in horizontally extended three-dimensional Rayleigh-Bénard convection flows are investigated in controlled laboratory experiments in water at Prandtl number Pr = 7. A Rayleigh-Bénard cell with square cross-section, aspect ratio Γ = l/h = 25, side length l and height h is used. Three different Rayleigh numbers in the range 10^5 < Ra < 10^6 are considered. The cell is accessible optically, such that thermochromic liquid crystals can be seeded as tracer particles to monitor simultaneously temperature and velocity fields in a large section of the horizontal mid-plane for long time periods of up to 6 h, corresponding to approximately 10^4 convective free-fall time units. The joint application of stereoscopic particle image velocimetry and thermometry opens the possibility to assess the local convective heat flux fields in the bulk of the convection cell and thus to analyse the characteristic large-scale transport patterns in the flow. A direct comparison with existing direct numerical simulation data in the same parameter range of Pr, Ra and Γ reveals the same superstructure patterns and global turbulent heat transfer scaling Nu(Ra). Slight quantitative differences can be traced back to violations of the isothermal boundary condition at the extended water-cooled glass plate at the top. The characteristic scales of the patterns fall into the same size range, but are systematically larger. It is confirmed experimentally that the superstructure patterns are an important backbone of the heat transfer. The present experiments enable, furthermore, the study of the gradual evolution of the large-scale patterns in time, which is challenging in simulations of large-aspect-ratio turbulent convection.
https://doi.org/10.1017/jfm.2022.538
Anisotropy of the electric field gradient in two-dimensional α-MoO3 investigated by 57Mn(57Fe) emission Mössbauer spectroscopy. - In: Crystals, ISSN 2073-4352, Bd. 12 (2022), 7, 942, S. 1-13
Van der Waals α-MoO3 samples offer a wide range of attractive catalytic, electronic, and optical properties. We present herein an emission Mössbauer spectroscopy (eMS) study of the electric-field gradient (EFG) anisotropy in crystalline free-standing α-MoO3 samples. Although α-MoO3 is a two-dimensional (2D) material, scanning electron microscopy shows that the crystals are 0.5-5-µm thick. The combination of X-ray diffraction and micro-Raman spectroscopy, performed after sample preparation, provided evidence of the phase purity and crystal quality of the samples. The eMS measurements were conducted following the implantation of 57Mn (t1/2 = 1.5 min), which decays to the 57Fe, 14.4 keV Mössbauer state. The eMS spectra of the samples are dominated by a paramagnetic doublet (D1) with an angular dependence, pointing to the Fe2+ probe ions being in a crystalline environment. It is attributed to an asymmetric EFG at the eMS probe site originating from strong in-plane covalent bonds and weak out-of-plane van der Waals interactions in the 2D material. Moreover, a second broad component, D2, can be assigned to Fe3+ defects that are dynamically generated during the online measurements. The results are compared to ab initio simulations and are discussed in terms of the in-plane and out-of-plane interactions in the system.
https://doi.org/10.3390/cryst12070942
Phase estimation of single tones next to modulated signals in the medium frequency R-mode system. - In: IEEE access, ISSN 2169-3536, Bd. 10 (2022), S. 73309-73316
Position, navigation, and timing information are critical to today’s infrastructures; as a result, the possibility of estimating ranges is being explored in more and more radio systems. One way to achieve this is to extend the modulation with time-synchronised aiding carriers and to estimate their phase at the receiver side. In this paper, we present two ways to minimise the negative influence of the modulation on the phase estimation. We show that the classical maximum likelihood estimator is still an efficient estimator for our problem, using a medium-frequency R-Mode signal as an example, and is therefore used in receiver designs. We then describe two possible ways to precondition the signal to increase the accuracy for short observations. As a first approach, we describe how window functions can positively change the signal-to-noise ratio for our estimation. As a second approach, we show the use of a narrowband bandpass filter. Finally, we show that these approaches, applied to real measurements, improve the variance of the estimate by up to two orders of magnitude.
https://doi.org/10.1109/ACCESS.2022.3190544
The interplay of biomimetics and biomechatronics. - In: Biomimetics, ISSN 2313-7673, Bd. 7 (2022), 3, 96, S. 1-9
Biomechatronics is an engineering subject in which biomimetics as a method is one of its two supporting pillars: biology for engineering, or Bio4Eng. This is contrasted with biocompatible design, or Eng4Bio, examples of which are human-serving systems, such as exoskeletons, and biomedical engineering. The paper aims to illustrate that the research fields of biomimetics, biomechatronics, and biomedical engineering are not in competition but mutually supportive. The current attempts to place biomechatronics under the umbrella of biomimetics or biomedical engineering are therefore not expedient; they deprive the subject of its strength of combining Bio4Eng and Eng4Bio at any time in a task-related manner. In addition to research and development, however, the training of the specialists supporting the subjects must not be disregarded and is therefore described based on a proven design.
https://doi.org/10.3390/biomimetics7030096
Magnetic hybrid materials interact with biological matrices. - In: Magnetic hybrid-materials, (2022), S. 681-738
Magnetic hybrid materials are a promising group of substances. Their interaction with matrices is challenging with regard to the underlying physical and chemical mechanisms. But thinking matrices as biological membranes or even structured cell layers they become interesting with regard to potential biomedical applications. Therefore, we established in vitro blood-organ barrier models to study the interaction and processing of superparamagnetic iron oxide nanoparticles (SPIONs) with these cellular structures in the presence of a magnetic field gradient. A one-cell-type-based blood-brain barrier model was used to investigate the attachment and uptake mechanisms of differentially charged magnetic hybrid materials. Inhibition of clathrin-dependent endocytosis and F-actin depolymerization led to a dramatic reduction of cellular uptake. Furthermore, the subsequent transportation of SPIONs through the barrier and the ability to detect these particles was of interest. Negatively charged SPIONs could be detected behind the barrier as well as in a reporter cell line. These observations could be confirmed with a two-cell-type-based blood-placenta barrier model. While positively charged SPIONs heavily interact with the apical cell layer, neutrally charged SPIONs showed a retarded interaction behavior. Behind the blood-placenta barrier, negatively charged SPIONs could be clearly detected. Finally, the transfer of the in vitro blood-placenta model in a microfluidic biochip allows the integration of shear stress into the system. Even without particle accumulation in a magnetic field gradient, the negatively charged SPIONs were detectable behind the barrier. In conclusion, in vitro blood-organ barrier models allow the broad investigation of magnetic hybrid materials with regard to biocompatibility, cell interaction, and transfer through cell layers on their way to biomedical application.
Compositional dependence of epitaxial L10-Mnx Ga magnetic properties as probed by 57Mn/Fe and 119In/Sn emission Mössbauer spectroscopy. - In: Physica status solidi, ISSN 1521-3951, Bd. 259 (2022), 7, 2200121, S. 1-11
The magnetic properties of Mn x Ga alloys critically depend on composition x, and the atomic-scale origin of those dependences is still not fully disclosed. Molecular beam epitaxy has been used to produce a set of Mn x Ga samples (x = 0.7 ÷ 1.9) with strong perpendicular magnetic anisotropy, and controllable saturation magnetization and coercive field depending on x. By conducting 57Mn/Fe and 119In/Sn emission Mössbauer spectroscopy at ISOLDE/CERN, the Mn and Ga site-specific chemical, structural, and magnetic properties of Mn x Ga are investigated as a function of x, and correlated with the magnetic properties as measured by superconducting quantum interference device magnetometry. Hyperfine magnetic fields of Mn/Fe (either at Mn or Ga sites) are found to be greatly influenced by the local strain induced by the implantation. However, In/Sn probes show clear angular dependence, demonstrating a huge transferred dipolar hyperfine field to the Ga sites. A clear increase of the occupancy of Ga lattice sites by Mn for x > 1 is observed, and identified as the origin for the increased antiferromagnetic coupling between Mn and Mn at Ga sites that lowers the samples' magnetization. The results shed further light on the atomic-scale mechanisms driving the compositional dependence of magnetism in Mn x Ga.
https://doi.org/10.1002/pssb.202200121
Hydrogenated TiO2 nanoparticles loaded with Au nanoclusters demonstrating largely enhanced performance for electrochemical reduction of nitrogen to ammonia. - In: Energy technology, ISSN 2194-4296, Bd. 10 (2022), 7, 2200085, S. 1-9
Pristine TiO2/Au (P-TiO2/Au) is modified by hydrogen plasma (H-TiO2/Au) or hydrogen and oxygen plasma (H-O-TiO2/Au) treatment, and then used as electrochemical catalysts for nitrogen reduction reaction (NRR). H-TiO2/Au shows enhanced performance for the NRR process compared with both P-TiO2/Au and H-O-TiO2/Au. After hydrogenation treatment, some disordered regions on the surface of TiO2 nanoparticles are formed, and a large number of oxygen vacancies are incorporated into the TiO2 crystalline structures. When the samples are used as catalysts for electrochemical NRR, the yield of NH3 of H-TiO2/Au is about ten times compared to that of P-TiO2/Au and about three times that of H-O-TiO2/Au, while the highest Faradaic efficiency of 2.7% is also obtained at the potential of -0.1 V for the H-TiO2/Au catalyst. The density functional theory (DFT) calculation results confirm that H-TiO2/Au with oxygen vacancies and the disordered surface layer is much preferred energetically for the NRR process. It proves that enhanced adsorption of N2 molecules on the catalyst and reduced reaction barriers due to the presence of defects play an important role in improving catalysts’ performances. The results show that the plasma hydrogenation technique can be used as an efficient method to modify catalysts for electrochemical NRR processes.
https://doi.org/10.1002/ente.202200085
PPDN and NTCDA radical anions formation in EMIM-DCA, BMIM-BF4 EMIM-Ac ionic liquid solutions under the steady state UV and Vis light illumination: a combined X-, K-band EPR and DFT study. - In: Journal of molecular liquids, ISSN 1873-3166, Bd. 362 (2022), 119631
The radical anion of Pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN) in blends with imidazolium based room temperature ionic liquids (RTIL): EMIM-DCA, BMIM-BF4, EMIM-Ac has been detected by X-band continues wave (CW) electron paramagnetic resonance (EPR) under steady state Xe-lamp illumination in the temperature interval from 190 to 340 K. The radical anion of 1,4,5,8-Naphthalenetetracarboxylic dianhydride (NTCDA) was registered by X- and K-band CW EPR at room temperature under the visible light CW diode laser operated at 532 nm, and Xe-lamp as well. The experimental hyperfine coupling data of both anion radicals were confirmed by DFT calculation. The formation of PPDN•- NTCDA•- and fullerene derivative (FD) radical anions is attributed to the photoelectron transfer from an IL anion to PPDN, NTCDA and FD electron acceptors. Here, the electron transfer leads to an irreversibility of these reactions due to photo-induced decomposition of the IL anions in the presence of an effective electron acceptor and is supported in the above RTILs solutions by means of EPR. For the indirect confirmation of the EMIM-DCA, EMIM-AC, BMIM-BF4 anion degradation in solutions with PPDN and NTCDA up to the transient radical state, similar data of acetate anion [OCOCH3]- decomposition, under CW Xe-Lamp photolysis resulting in •CH3 formation and its stabilization at 77 K in EMIM-Ac suspension with some FD dissolved in DCB are introduced as well. However, the main goal of this study is dedicated to the features of rotational and translational diffusion kinetics of PPDN and NTCDA radical anions in IL solutions as well to the evaluation of their application as a spin probes in ILs study in liquid phase.
https://doi.org/10.1016/j.molliq.2022.119631
Design of an enhanced mechanism for a new Kibble balance directly traceable to the quantum SI. - In: EPJ Techniques and Instrumentation, ISSN 2195-7045, Bd. 9 (2022), 1, 7, S. 1-18
The "Quantum Electro-Mechanical Metrology Suite" (QEMMS) is being designed and built at the National Institute of Standards and Technology. It includes a Kibble balance, a graphene quantum Hall resistance array and a Josephson voltage system, so that it is a new primary standard for the unit of mass, the kilogram, directly traceable to the International System of Units (SI) based on quantum constants. We are targeting a measurement range of 10 g to 200 g and optimize the design for a relative combined uncertainty of for masses of 100 g. QEMMS will be developed as an open hardware and software design. In this article, we focus on the design of an enhanced moving and weighing mechanism for the QEMMS based on flexure pivots.
https://doi.org/10.1140/epjti/s40485-022-00080-3
Influence of tool and welding parameters on the risk of wormhole defect in aluminum magnesium alloy welded by bobbin tool FSW. - In: Metals, ISSN 2075-4701, Bd. 12 (2022), 6, 969, S. 1-14
Bobbin tool friction stir welding (BTFSW) utilizes a special tool that possesses two shoulders interconnected by a pin instead of one: the top shoulder and the pin in the conventional FSW tool. This greatly simplifies the kinematics in the otherwise complicated setup of FSW since the bottom shoulder forms the bottom surface of the weld, without the need for a backing plate. Moreover, the tool enters the base metal sideways and travels, forming the joint in a straight line while rotating, without the need for downward and upward motion at the beginning and end of the process. This paper presents a study on the BTFSW tool geometry and parameters on the risk of wormhole defect formation in the AA5005 aluminum–magnesium alloy and the wormhole effect on mechanical properties. It was shown that higher stress imposed by the tool geometry on the joint has a significant influence on heating, an effect similar to the increased rotational speed. Optimal kinematic and geometrical tool properties are required to avoid wormhole defects. Although weld tensile strengths were lower (between ˜111 and 115 MPa) compared with a base metal (137 MPa), the ductile fracture was obtained. Furthermore, all welds had a higher impact strength (between ˜20.7 and 27.8 J) compared with the base material (˜18.5 J); it was found that the wormhole defect only marginally influences the mechanical properties of welds.
https://doi.org/10.3390/met12060969