3,095 research outputs found
Structured Analysis and Review of Filter-Based Control Strategies for Hybrid Energy Storage Systems
Hybrid energy storage systems (HESS), i.e., the combination of two different energy storage technologies, are widely discussed as a promising solution for energy storage problems. A common control scheme to allocate the power between these storages and the subject of this study is filter-based control, where a filter splits the input signal into a low-frequency and high-frequency part. It provides robust results and easy implementation, although more advanced strategies may perform better. Many publications use this controller for specific problems, but a structured analysis of this controller type that quantifies the advantages and disadvantages, traits, and setbacks is missing. This work fills this gap and structures, summarizes, and provides mathematical background and guidelines on filter-based control of hybrid energy storage systems. Numerical simulations are performed to quantify the impact of design variables, parameters, or the input signal by using a linear storage model with efficiency and self-discharge rate and a low-pass filter controller with constant energy feedback as a representative subtype of this control scheme. The present work proves the high cycle-reduction capabilities of filter-controlled HESS at the cost of overdimensioning compared to more advanced control strategies. It demonstrates that using a high-efficiency, high-power storage with a low self-discharge rate and high-energy storage leads to smaller overall dimensioning and losses than a single storage system. The study identifies the feedback factor of the controller as the most impacting design variable
New Dimensions in Catalysis Research with Hard XâRay Tomography
The structure and function of solid catalysts are inseparably linked at length scales from nm to cm and beyond. Hard X-ray tomography offers unique potential for spatially-resolved characterization by combining flexible spatial resolution with a range of chemical contrasts. However, the full capabilities of hard X-ray tomography have not been widely explored in the catalysis community. This review highlights modern advances in hard X-ray tomography using synchrotron radiation. Case studies from model to technical scale illustrate the bright future of X-ray tomography in catalysis research
Thermally stable mesoporous tetragonal zirconia through surfactant-controlled synthesis and Si-stabilization
Thermally stable, highly mesoporous Si-stabilized ZrOâ was prepared by solâgel-synthesis. By utilizing the surfactant dodecylamine (DDA), large mesopores with a pore width of âŒ9.4 nm are formed. Combined with an NHâ-treatment on the hydrogel, a high specific surface area of up to 225 mÂČ gâ»Âč and pore volume up to 0.46 cmÂł gâ»Âč are obtained after calcination at 973 K. The individual contributions of Si-addition, DDA surfactant and the NHâ-treatment on the resulting pore system were studied by inductively coupled plasma with optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), Nâ sorption, and transmission electron microscopy (TEM). Electron tomography was applied to visualize and investigate the mesopore network in 3D space. While Si prevents the growth of ZrOâ crystallites and stabilizes the t-ZrOâ phase, DDA generates a homogeneous mesopore network within the zirconia. The NHâ-treatment unblocks inaccessible pores, thereby increasing specific surface area and pore volume while retaining the pore width distribution
Harte RöntgenâNanotomographie zur 3DâAnalyse der Verkokung in Nickelâbasierten Katalysatoren
Das VerstĂ€ndnis der Katalysatordesaktivierung durch Verkokung ist entscheidend fĂŒr ein wissensbasiertes Katalysator- und Prozessdesign bei Reaktionen mit Kohlenstoffverbindungen. Die Katalysatorverkokung wird dabei typischerweise durch Post-Mortem-Analyse untersucht. In der vorliegenden Arbeit wird ptychographische Röntgentomographie (PXCT) zur Analyse von kĂŒnstlich verkokten Ni/Al2O3-Katalysatoren fĂŒr die CO2-Methansierung und CH4-Trockenreformierung verwendet. PXCT liefert dabei 3D-Informationen der lokalen Elektronendichte mit ca. 80â
nm Auflösung und ermöglicht somit die Visualisierung und Untersuchung der AusprĂ€gung der Verkokung in Katalysatorpartikeln mit einem Durchmesser von ca. 40â
ÎŒm. Die Verkokung wurde hauptsĂ€chlich im nanoporösen Festkörper identifiziert und konnte nicht in den aufgelösten Makroporen gefunden werden. Die Kohlenstoffbildung wurde unabhĂ€ngig dazu mittels operando Raman-Spektroskopie bestĂ€tigt. PXCT wird als aufkommende Charakterisierungstechnik hervorgehoben, die eine nanoskalige Identifizierung, Lokalisierung und möglicherweise Quantifizierung von verschiedenen DesaktivierungsphĂ€nomenen mit 3D-Auflösung in kompletten Katalysatorpartikeln ermöglicht
Hard X-Ray Nanotomography for 3D Analysis of Coking in Nickel-Based Catalysts
Understanding catalyst deactivation by coking is crucial for knowledge-based catalyst and process design in reactions with carbonaceous species. Post-mortem analysis of catalyst coking is often performed by bulk characterization methods. Here, hard X-ray ptychographic computed tomography (PXCT) was used to study Ni/Al2O3 catalysts for CO2 methanation and CH4 dry reforming after artificial coking treatment. PXCT generated quantitative 3D maps of local electron density at ca. 80 nm resolution, allowing to visualize and evaluate the severity of coking in entire catalyst particles of ca. 40 ÎŒm diameter. Coking was primarily revealed in the nanoporous solid, which was not detectable in resolved macropores. Coke formation was independently confirmed by operando Raman spectroscopy. PXCT is highlighted as an emerging characterization tool for nanoscale identification, co-localization, and potentially quantification of deactivation phenomena in 3D space within entire catalyst particles
Hard Xâray Nanotomography for 3D Analysis of Coking in Nickelâbased Catalysts
Understanding catalyst deactivation by coking is crucial for knowledge-based catalyst and process design in reactions with carbonaceous species. Post-mortem analysis of catalyst coking is often performed by bulk characterization methods. Here, hard X-ray ptychographic computed tomography (PXCT) was used to study Ni/AlO catalysts for CO methanation and CH dry reforming after artificial coking treatment. PXCT generated quantitative 3D maps of local electron density at ca. 80â
nm resolution, allowing to visualize and evaluate the severity of coking in entire catalyst particles of ca. 40â
ÎŒm diameter. Coking was primarily revealed in the nanoporous solid, which was not detectable in resolved macropores. Coke formation was independently confirmed by operando Raman spectroscopy. PXCT is highlighted as an emerging characterization tool for nanoscale identification, co-localization, and potentially quantification of deactivation phenomena in 3D space within entire catalyst particles
Complementary operando insights into the activation of multicomponent selective propylene oxidation catalysts
Two BiâMoâCoâFeâO catalysts were synthesized by flame spray pyrolysis and tested for their catalytic performance in selective oxidation of propylene to acrolein. Pronounced structural changes during temperatureâprogrammed oxidation and reaction were observed by operando Xâray absorption spectroscopy, Xâray diffraction, Raman spectroscopy, and thermogravimetric analysis. During oxidative treatment, mainly binary oxide phases (αâBiMoO, ÎČâCoMoO, Fe (MoO)) were observed, but single (MoO) or ternary (Bi (FeO)(MoO)) oxides also formed depending on the relative elemental catalyst composition. During propylene oxidation, the reduction of Fe to Fe led to a strong rise in activity and induced further phase transformations. MoO was found to be unselective towards acrolein but was essential in binding other single oxides. The formation of ÎČâCoFeMoO and Bi (FeO)(MoO) as well as their synergistic interplay with αâBiMoO are key factors for high performance. The combination of complementary operando methods was crucial to reveal new structureâactivity/selectivity correlations, therefore bridging the knowledge gap between simplified model systems and complex applied catalysts
Charm mass effects in the static energy computed in 2+1+1 flavor lattice QCD
We report our analysis for the static energy in (2+1+1)-flavor QCD over a
wide range of lattice spacings and several quark masses. We obtain results for
the static energy out to distances of nearly 1 fm, allowing us to perform a
simultaneous determination of the lattice scales , and as well
as the string tension, . While our results for and
agree with published (2+1)-flavor results, our result for
differs significantly from the value obtained in the (2+1)-flavor
case, likely due to the effect of the charm quark. We study in detail the
effect of the charm quark on the static energy by comparing our results on the
finest lattices with the previously published (2+1)-flavor QCD results at
similar lattice spacing. The lattice results agree well with the two-loop
perturbative expression of the static energy incorporating finite charm mass
effects.Comment: 9 pages, 4 figures, The 39th International Symposium on Lattice Field
Theory (Lattice2022),8-13 August, 2022,Bonn, German
QuantumFDTD - A computational framework for the relativistic Schrödinger equation
We extend the publicly available quantumfdtd code. It was originally intended for solving the time-independent three-dimensional Schrödinger equation via the finite-difference time-domain (FDTD) method and for extracting the ground, first, and second excited states. We (a) include the case of the relativistic Schrödinger equation and (b) add two optimized FFT-based kinetic energy terms for the non-relativistic case. All the three new kinetic terms are computed using Fast Fourier Transform (FFT).We release the resulting code as version 3 of quantumfdtd. Finally, the code now supports arbitrary external filebased potentials and the option to project out distinct parity eigenstates from the solutions. Our goal is quark models used for phenomenological descriptions of QCD bound states, described by the three-dimensional Schrödinger equation. However, we target any field where solving either the non-relativistic or the relativistic three-dimensional Schrödinger equation is required
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