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<p> A physical model for redox flow batteries is developed to estimate performance for any chemistry using parameters such as electrolyte conductivity and kinetic rate constants. The model returns the performance as a function of flow rate, current density, and state of charge. Two different models are developed to estimate the current density distribution throughout the electrode in order to evaluate physical performance of the battery. This is done using electrochemical parameters such as conductivity and kinetic rate constant. The models are analytical in order to produce a computationally cheap algorithm that can be used in optimization routines. This allows for evaluating the economic performance of redox flow batteries, and optimization of cost. The models are validated vs data and found to accurately predict performance in a V-V system for a wide variety of operating conditions.</p>

<p> During the combustion of carbonaceous fuels under rich conditions, incomplete combustion will lead to a fraction of fuel&rsquo;s carbon being converted into carbonaceous particulate known as soot. The particle inception process is believed to occur at the transition from gas-phase to solid-phase species and is known to involve polyaromatic hydrocarbons (PAH). While parts of the soot formation mechanism are well-understood, this particle inception process lacks the same level of experimental rigor. A combination of in situ and ex situ optical spectroscopy methods have allowed us to fill this experimental void. Tauc/Davis-Mott analysis using a supercontinuum light source was used to map out the experimentally determined optical band gap through a range of laminar diffusion flames including both gas and liquid phase fuels. The average optical band gap observed across all of the flames was 2.06 &plusmn;0.03eV. Semi-empirical (ZINDO/S) and quantum mechanical (DFT) computations were performed to relate the experimentally determined optical band gap to the HOMO-LUMO gap in a variety of PAH. The average PAH sizes in these flame systems corresponded to structures of 11 &plusmn; 4 rings and conjugation lengths between 0.85 &plusmn; 0.11 nm. Raman spectroscopy of thermophoretically sampled soot supported these results concluded finding a consistent conjugation length of 0.86 &plusmn; 0.10 nm was observed throughout the entire flame system . FTIR spectroscopy of thermophoretically sampled soot in the same flame system found the prevalence of both aromatic and aliphatic compounds throughout the entire flame, but was not able to conclude the nature of the aliphatic species. The conclusions from this work indicate that the particle inception occurs with structures about the size of ovalene and this size seems to be consistent across of a variety of fuels and sooting levels. Additionally, the consistency of conjugation lengths and optical band gaps determined throughout the flame systems, with increasing soot volume fractions indicates that further mass growth of the soot particulates occurs through aggregation processes.</p>

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Niobium rf superconductivity is a near-surface phenomenon because of the shallow rf penetration depth. Accordingly, the performance of Nb SRF accelerator cavities is strongly impacted by the topmost few nanometers interior surface, especially as impacted by the final surface conditioning treatments.;Surface topography impacts performance through local loss of superconductivit caused by intrusion of the rf magnetic field, which is enhanced at sharp protrusions. "Sharpness" comprises both vertical and lateral aspects, requiring development a new characterization approach beyond the familiar roughness measurements (Ra, Rz), which view only the vertical component. Stylus profilomety and atomic force microscopy traces view surface topography from mm size to near atomic dimensions. Power spectral density analysis combines data across this whole dimensional scale, so that the effect of preparation variables on topography has been studied systematically for the first time.;Surface chemistry impacts performance through the presence of a complex surface oxide structure and the response of the surface to post-treatments, notably low temperature baking (e.g., 125??C, 24 hrs). Previous XPS studies consistently found that the surface chiefly comprises a few nm of Nb2O5 on top of Nb metal, with small amount of Nb suboxides near the interface. Efforts to unambiguously discern the variation of composition with depth in the surface region by angle-resolved XPS have been confounded by the effect of surface roughness. The problem was avoided here by, for the first time, using a synchrotron source to vary x-ray photon energy at fixed take-off angle, obtaining a range of sample depths in a fixed column of material spanning the oxide layer thickness. One result is that variation of etching practice chiefly affects the thickness of the top Nb2O5 layer, but the sub-oxide accommodation zone at the interface remains substantially constant. A second is that low temperature baking in vacuum results in significant thinning and reduction of the oxide layer, which is completely recovered on subsequent air exposure without loss of the SRF performance improvement.;The effect of the most commonly employed treatment-BCP on polycrystalline niobium sheet over a range of realistic solution flow rates has been examined through multiple surface characterization techniques. The surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of Nb2O5, whose thickness increases with solution flow rate to a maximum of 1.3∼1.4 times that resulting from static solution.;Electropolishing is believed to be an effective technique to treat niobium cavity surfaces for achieving reproducibly high performance SRF cavities. However the operation condition is basically optimized through practical processing. By using improved electrochemical techniques, the temperature, flow rate and HF concentration dependence of each potential were indentified. The first use of electrochemical impedance spectroscopy (EIS) on this system was reported. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in hydrofluoric sulfuric acid electrolyte and do not supports either the porous salt film or the absorbate-acceptor mechanism.

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