Raman-modes of index-identified free-standing single-walled carbon nanotubes

Using electron diffraction on free-standing single-walled carbon nanotubes we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3nm. On the same free-standing tubes we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7nm) these measurements confirm previously established radial breathing mode frequency versus diameter relations, and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned.Comment: 4 pages, 4 figures, +additional materials (select PostScript to obtain it

Energy and Exergy Assessment of Renewable Energy Storage using Iron as Energy Carrier

The transformation to a climate-neutral electricity economy makes the sustainable generation of electricity from renewable energies a key technology. However, the widespread use of renewable energy faces several challenges, especially its volatility and locally limited availability. Addressing the temporal and geographic mismatch between renewable energy supply and demand is therefore crucial for a successful carbon-neutral electricity economy. Large-scale, transportable, and storable energy carriers are a key element in redressing this imbalance. Besides hydrogen-based fuels, metal fuels and iron in particular are promising alternatives to serve this purpose: electrical energy from renewable sources is stored by thermochemical reduction of iron oxides with green hydrogen and can be converted back into electricity by thermochemical oxidation (e.g., in retrofitted coal-fired power plants) spatially and temporally separated from the storage process. Despite the increasing interest in metal fuels, not many cycle analyses are available. This study provides quantitative and qualitative information on the thermodynamic performance of two thermodynamically controlled regeneration processes for iron oxides utilising a shaft furnace and a flash reactor, respectively. For the shaft furnace direct reduction of iron oxides energetic and exergetic efficiencies of 59.4% and 51.4 %, respectively, are determined. A sensitivity analysis indicates that energetic efficiencies up to 63.0% might be achievable within the model assumptions. The evaluation of the flash reactor direct reduction of iron oxides shows energetic and exergetic efficiencies of 68.5% and 59.9 %, respectively. In this case, optimal values based on sensitivity analyses lead to an energetic efficiency of 71.0% within the model assumptions. In addition to the use of commercial software, a modelling environment with direct access to mathematical optimisation techniques is in development and showcased for the flash reduction process leading to energetic efficiencies of 73.1 %. The developed models are the foundation for future thermoeconomic evaluations

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Advanced Exergy Analysis of the Flash Ironmaking Process

The growing demand for renewable energy highlights the importance of green energy carriers in mitigating the temporal and geographic imbalances between renewable energy supply and demand. Iron, as a metal fuel, offers a promising solution by enabling the storage of electrical energy from renewables through the thermochemical reduction of iron oxides with green hydrogen. This stored energy can be later converted back into electricity via thermochemical oxidation, such as in retrofitted coal-fired power plants. Transporting the iron/iron oxide in a closed cycle allows for spatial and temporal separation of renewable energy storage and release. To maximize the system efficiency of this energy-iron cycle, it is crucial to achieve high storage efficiencies during the thermochemical reduction of iron oxides. The flash ironmaking process is a promising method for this, as it allows for the reduction of fine iron oxide particles with green hydrogen without the need for pre- or post-treatment. Conventional exergy analyses, as well as advanced exergy analysis, are used to analyze the flash ironmaking process. The results reveal an exergetic system efficiency of 53.7 % for a defined base case, with the largest share of exergy destruction attributed to unavoidable exergy destruction at 82.2 % of the total exergy destruction. Additionally, most of the exergy destruction was endogenous at 89.4 % of the total exergy destruction. These assessments indicate that the overall potential for improvement of the reduction plant is moderate, and component improvements should be prioritized over structural improvements to reduce avoidable endogenous exergy destruction

Techno-Economic Optimization of an Innovative Plant for Sustainable Iron Reduction

Metal fuels such as iron represent potential energy carriers for large-scale storage and transport of renewable energy. In a circular process renewable energies can be stored in form of iron by thermochemical reduction of iron oxide and the required energy can be released via thermochemical oxidation, time and location independent from the storage process. While existing infrastructure such as coal-fired power plants could be retrofittedto meet the needs for the oxidation process, the conceptualization and construction of new infrastructure for the storage process by reduction is required. This opens up the possibility for a thorough techno-economic assessment of potential processes in order to ensure the optimal process design. Therefore, a techno-economic model of an innovative reduction plant utilizing the flash ironmaking technology for the reduction reactor is developed. The resulting mathematical model describes the operation of the reduction plant in dependence of design variables defining the plant components’ dimensions. These design variables together with further process variables are optimized using mathematical optimization with respect to an economic objective function, i.e. the levelized cost of iron, in order to obtain the economically optimal process design. Thorough analyses are performed to assess the impact of changing economic boundary conditions on the optimal process design. Numerical results demonstrate a strong dependence of the cost optimal design on the available renewable energy prices and the obtained levelized cost of iron varies between 0.05 $/kg iron and 0.68$/kg iron. Thus, choosing appropriate reduction locations with access to low renewable energy prices is crucial for the economic competitiveness of the considered process. The results further confirm an expected trade-off between total investment costs and yearly energy consumption of the plant components. With increasing cost for renewable energy, energetically more efficient system designs also become economically advantageous, i.e. an increase in the energetic efficiency from ηsys = 55.6% to ηsys = 69.3% is observable. The electrolyzer turns out to be the dominant plant component both, economically and energetically. Future work will take uncertainties into account to ensure a robust process design and couple the reduction plant to location specific renewable energy systems

Transient Generalized Chorea in Influenza A Encephalopathy

Background: Influenza A infections are a rare cause of movement disorders. Previously described patients have suffered from acute-onset myoclonus and/or dystonia or post-viral parkinsonism. Case Report: We present the case of a 74-year-old female patient with transient generalized chorea due to influenza A-mediated encephalopathy. Discussion: We discuss whether the clinical presentation and the magnetic resonance imaging changes may be attributable to cytokine-mediated encephalopathy or to direct cytotoxic effects of the virus. Additionally, we would like to make clinicians aware of this clinical sign in the context of viral encephalopathy

Pump System Test Instances and Electronical Pump Catalogues

This dataset contains relevant information for planning pump systems. This includes (i) the description of different test cases and their boundary conditions. It comprises (a) the pump system of an industrial cooling circuit and (b) several booster stations for different buildings as well as a test rig. These data are available as two .json files. Furthermore, (ii) electronic pump catalogues are provided. Standardised chemical pumps, pumps for booster stations of high-rise buildings and the pumps of the test rig including suitable frequency converters are described. The description includes the pump types, their characteristic curves and possible purchase prices. A total of 296 different pump types are specified. These data are available as three .csv files. The file ReadMe.md explains the data in more detail, especially the meaning of the individual columns of the .csv files. The data can be used to evaluate planning methods - especially algorithmically supported methods. For the mathematical optimisation of pump systems, the data of the cooling circuit and the standardised chemical pumps have been used in publication [2] and [3] and the data of the buildings and the test rig have been used in publications [1] and [2]. Further information on the pumps and test cases can be found in these publications. References: [1] - Tim M. Müller, Philipp Leise, Imke-Sophie Lorenz, Lena C. Altherr and Peter F. Pelz: Optimization and validation of pumping system design and operation for water supply in high-rise buildings. In: Optimization and Engineering 22.2 (2021), S. 643–686, DOI: https://doi.org/10.1007/s11081-020-09553-4. [2] - Tim M. Müller: Algorithmisch gestützte Planung dezentraler Pumpensysteme, PhD-Thesis, Technical University of Darmstadt, in preparation. [3] - Tim M. Müller, Jannik Neumann, Marvin M. Meck und Peter F. Pelz: Sustainable Cooling Cycles by Algorithmically Supported Design of Decentral Pumping Systems. Under Review in Applied Thermal Engineering (2022).Initial Versio