Controlled regulation of the transformation of carbon nanomaterials under H2 mixture atmosphere by arc plasma. - In: Chemical engineering science, Bd. 241 (2021), 116695
Im Titel ist "2" tiefgestellt
Hydrogen plays a pivotal role in carbon nanomaterials synthesis by arc plasma. However, the effect of hydrogen on morphological regulation of carbon nanomaterials has received little attention. In this paper, carbon nanomaterials synthesized under mixed H2/Ar, H2/N2, and Ar/N2 atmospheres with different ratios were investigated in detail to tackle the issue. Graphene, carbon nanocages, polyhedral graphite particles, amorphous carbon nanoballs, and carbon nanohorns underwent structural transformation as hydrogen content reduced. As a result of varying hydrogen concentration, the number of C-H bond sites at the edge of graphene islands differed, leading to the structural transformation of carbon nanomaterials originating from the formation of various types of precursors. Meanwhile, X-ray photoelectron spectroscopy results revealed that hydrogen impeded nitrogen doping because it tended to bond with electronegative nitrogen. Moreover, morphology control capability followed the order of H2 > N2 > Ar during the preparation of carbon nanomaterials through arc plasma under a mixed atmosphere.
https://doi.org/10.1016/j.ces.2021.116695
Self-heating of resistance thermometers for air temperature measurements with pulsed current supply :
Eigenerwärmung von Widerstandsthermometern für Lufttemperaturmessungen bei Impulstromspeisung. - In: Technisches Messen, ISSN 2196-7113, Bd. 88 (2021), 9, S. 556-561
Sehr präzise Lufttemperaturmessung in der Meteorologie oder in klimatisierten Innenräumen sind herausfordernd, weil Strahlungseinflüsse und die Eigenerwärmung der Widerstandsthermometer teilweise erhebliche Störeinflüsse sind. In unserem Artikel betrachten wir eine spezielle Stromspeisung und weisen nach, dass diese die Eigenerwärmung auf unter ein Millikelvin reduzieren kann. Für einen typischen, für den Außeneinsatz in meteorologischen Wetterstationen geeigneten und üblichen Fühleraufbau erfolgen Simulationen der durch den gepulsten elektrischen Messstrom auftretenden statischen und dynamischen Eigenerwärmung. Der transiente Verlauf der Eigenerwärmung hängt stärker vom inneren Aufbau des Fühlers als vom Wärmeübergangskoeffizienten zur umgebenden ruhenden Luft ab. Die mittlere statische Eigenerwärmung aus einem stark vereinfachten Modell passt gut zum simulierten transienten Verlauf. Die Methode der Impulsstromspeisung hat sich durch die beschriebenen Simulationen als sehr effektiv zur Verringerung der Eigenerwärmung von Widerstandsthermometern erwiesen.
https://doi.org/10.1515/teme-2021-0032
Electromagnetic interaction between a permanent magnet and a sphere moving in liquid metal. - In: Experiments in fluids, ISSN 1432-1114, Bd. 62 (2021), 5, 109, S. 1-16
We present a series of model experiments where an electrically non-conductive solid sphere moves inside a vertical column of liquid alloy GaInSn. The experimental setup consists of the liquid metal container, the sphere driving system and the permanent magnet with the attached force sensor. The sphere moves at a controllable constant velocity U0 and follows a straight route, which in turn generates a liquid metal flow around the sphere. This flow interacts with the localized magnetic field of the permanent magnet, and thus a weak reaction force on the magnet is generated. The force sensor attached on the magnet has a resolution of the order 10^-6. Upon elimination of high frequency noise, reproducible time-dependent signals for the forces on the magnet are obtained in the experiments for several Reynolds numbers Re between 160 and 2000. The force component Fz on the magnet parallel to the direction of particle motion exhibits a typical two-peak structure with different peak heights, whereas the transverse force component Fx resembles an antisymmetric pulse. The results demonstrate that the force sensor can detect the presence of a moving particle in a quiescent conducting liquid. They also show that the structure of the Fx signal can be reproduced with less variation and is less sensitive to the Reynolds number than the Fz signal. Moreover, the structure and magnitude of time-dependent Lorentz force signals can be reasonably predicted by a numerical model.
https://doi.org/10.1007/s00348-021-03209-4
Electrical voltage by electron spin-vorticity coupling in laminar ducts. - In: Physical review fluids, ISSN 2469-990X, Bd. 6 (2021), 4, 043703, insges. 14 S.
We report a linear scaling law for an electrical voltage as a function of the pressure drop in capillary pipes and ducts. This voltage is generated by a process which is termed spin hydrodynamic generation (SHDG), a result of the collective electron spin-coupling to the vorticity field in the laminar flow in combination with an inverse spin-Hall effect. We study this phenomenon in laminar duct flows with different width-to-height aspect ratios ranging from 1 (square ducts) to infinite (two dimensional channels). First, we analytically solve the governing Valet-Fert spin diffusion equations for the SHDG by means of the method of small parameters together with proper boundary conditions for the set of inhomogeneous elliptic partial differential equations. Second, the proposed linear scaling law is validated through a series of experiments using capillary tubes with rectangular and square cross sections. The experimental results show very good agreement to the analytically found scaling law. A subsequent substitution of the bulk velocity of the laminar wall-bounded flows by the pressure drop reveals a universal scaling law for the electrical voltage that incorporates all pipe and duct geometries which we could study in our experiments. Finally, the efficiency of the system is estimated for circular pipes, rectangular and square ducts. This study shows that the efficiency of a spin hydrodynamic generator is the same for a circular pipe and a square duct with the same diameter and height, respectively. Hence, due to the ease of manufacturing and the possibility to scale the experiments up to parallel settings in a compact form, micro-channels with a square cross section seem to be the optimum for a spin hydrodynamic generator.
https://doi.org/10.1103/PhysRevFluids.6.043703
Niobium neuron: RSFQ based bio-inspired circuit. - In: IEEE transactions on applied superconductivity, ISSN 1558-2515, Bd. 31 (2021), 5, 1800505, insges. 5 S.
Neuromorphic and bio-inspired circuits have reached considerable attention since Moore's Law is coming to its limitations. Information processing in mammalian brains takes place in a far more energy-efficient manner and significantly faster than in the best computing architecture nowadays. We propose an approach to bring those benefits to a superconducting information processing circuit. Since the computation in a neuronal network is considered as analogue and the computation as digital, the design is grown around a Josephson comparator with its inherent non-linearity in the transfer function as the central information processing unit. Furthermore, a modified version of the Josephson Transmission Line is used to realize an adaptable coupling between neuron cells. This circuit design benefits of the noise in a 4.2 K environment and is therefore more resilient to noise and switching errors than conventional digital circuits. The proposed circuit behavior in a 2-neuron configuration and the integration in a network topology will be investigated.
https://doi.org/10.1109/TASC.2021.3063212
Enhanced potassium storage capability of two-dimensional transition-metal chalcogenides enabled by a collective strategy. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 13 (2021), 16, S. 18838-18848
Potassium-ion batteries (PIBs) have been considered as a promising alternative to lithium-ion batteries due to their merits of high safety and low cost. Two-dimensional transition-metal chalcogenides (2D TMCs) with high theoretical specific capacities and unique layered structures have been proven to be amenable materials for PIB anodes. However, some intrinsic properties including severe stacking and unsatisfactory conductivity restrict their electrochemical performance, especially rate capability. Herein, we prepared a heterostructure of high-crystallized ultrathin MoSe2 nanosheet-coated multiwall carbon nanotubes and investigated its electrochemical properties with a view to demonstrating the enhancement of a collective strategy for K storage of 2D TMCs. In such a heterostructure, the constructive contribution of CNTs not only suppresses the restacking of MoSe2 nanosheets but also accelerates electron transport. Meanwhile, the MoSe2 nanosheets loaded on CNTs exhibit an ultrathin feature, which can expose abundant active sites for the electrochemical reaction and shorten K+ diffusion length. Therefore, the synergistic effect between ultrathin MoSe2 and CNTs endows the resulting nanocomposite with superior structural and electrochemical properties. Additionally, the high crystallinity of the MoSe2 nanosheets further leads to the improvement of electrochemical performance. The composite electrode delivers high-rate capacities of 209.7 and 186.1 mAh g-1 at high current densities of 5.0 and 10.0 A g-1, respectively.
https://doi.org/10.1021/acsami.1c01891
Reclassification of Haloactinobacterium glacieicola as Occultella glacieicola gen. nov., comb. nov., of Haloactinobacterium album as Ruania alba comb. nov, with an emended description of the genus Ruania, recognition that the genus names Haloactinobacterium and Ruania are heterotypic synonyms and description of Occultella aeris sp. nov., a halotolerant isolate from surface soil sampled at an ancient copper smelter. - In: International journal of systematic and evolutionary microbiology, ISSN 1466-5034, Bd. 71 (2021), 4, 004769
In the course of screening the surface soils of ancient copper mines and smelters (East Harz, Germany) an aerobic, non-motile and halotolerant actinobacterium forming small rods or cocci was isolated. The strain designated F300T developed creamy to yellow colonies on tryptone soy agar and grew optimally at 28 ˚C, pH 7-8 and with 0.5-2% (m/v) NaCl. Its peptidoglycan was of type A4α l-Lys-l-Glu (A11.54). The menaquinone profile was dominated by MK-8(II, III-H4) and contained minor amounts of MK-8(H2), MK-8(H6) and MK-9(H4). The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, mono and diacylated phosphatidylinositol dimannosides, and components that were not fully characterized, including two phospholipids, two glycolipids and an uncharacterized lipid. Major whole-cell sugars were rhamnose and ribose. The fatty acid profile contained mainly iso and anteiso branched fatty acids (anteiso-C15:0, iso-C14:0) and aldehydes/dimethylacetals (i.e. not fatty acids). Sequence analysis of its genomic DNA and subsequent analysis of the data placed the isolate in the group currently defined by members of the genera Ruania and Haloactinobacterium (family Ruaniaceae , order Micrococcales ) as a sister taxon to the previously described species Haloactinobacterium glacieicola , sharing an average nucleotide identity and average amino acid identity values of 85.3 and 85.7%, respectively. Genotypic and chemotaxonomic analyses support the view that strain F300T (=DSM 108350T=CIP 111667T) is the type strain of a new genus and new species for which the name Occultella aeris gen. nov., sp. nov. is proposed. Based on revised chemotaxonomic and additional genome based data, it is necessary to discuss and evaluate the results in the light of the classification and nomenclature of members of the family Ruaniaceae , i.e. the genera Haloactinobacterium and Ruania . Consequently, the reclassification of Haloactinobacterium glacieicola as Occultella glacieicola comb. nov. and Haloactinobacterium album as Ruania alba comb. nov., with an emended description of the genus Ruania are proposed.,
https://doi.org/10.1099/ijsem.0.004769
Broadband femtosecond spectroscopic ellipsometry. - In: Review of scientific instruments, ISSN 1089-7623, Bd. 92 (2021), 3, S. 033104-1-033104-14
We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump-probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV-3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues.
https://doi.org/10.1063/5.0027219
Measurement uncertainty 2020 :
Messunsicherheit 2020. - In: Technisches Messen, ISSN 2196-7113, Bd. 88 (2021), 2, S. 59-60
https://doi.org/10.1515/teme-2021-0003
High-efficiency photothermal water evaporation using broadband solar energy harvesting by ultrablack silicon structures. - In: Advanced energy & sustainability research, ISSN 2699-9412, Bd. 2 (2021), 4, 2000083, S. 1-9
Development of broadband absorption materials for solar energy harvesting is an important strategy to address global energy issues. Herein, it is demonstrated that an ultrablack silicon structure with abundant surface texturing can absorb about 98.7% solar light within the wavelength range of 300 to 2500 nm, i.e., a very large range and amount. Under 1 sun irradiation, the ultrablack silicon sample's surface temperature can increase from 21.2 to 51.2 ˚C in 15 min. During the photothermal water evaporation process, the ultrablack silicon sample's surface temperature can still reach a highest temperature of 43.2 ˚C. The average photothermal conversion efficiency (PTCE) can be as high as 72.96%. The excellent photothermal performance to the excellent light-trapping ability of the pyramidal surface nanostructures during solar illumination, which leads to extremely efficient absorption of light, is attributed. In addition, the large water contact area also enables fast vapor transport. The stability of the photothermal converter is also examined, presenting excellent structure and performance stabilities over 10 cycles. This indicates that the ultrablack Si absorber can be a promising photothermal conversion material for seawater desalination, water purification, photothermal therapy, and more.
https://doi.org/10.1002/aesr.202000083