Soot in combustion simulations

Journal ArticleSoot is the dominant source of radiative heat transfer from most practical flames. A review is presented of historical, empirical modelling approaches for estimating heat flux from fires and flames. These historical methods have drawn on empiricism to address the role of soot while seeking methods for including the multi-scale effects of soot formation and flame structure. Both soot concentration and flame temperature have been seen to be local phenomena with dimensions on the order of the diffusion and chemical (Batchelor) scales of the flame. The correlation between the local soot volume fraction and the local temperature field is needed for determining the radiant heat flux from the flame. By using high performance computers (hundreds to thousands of processors) Large Eddy Simulations (LES) can resolve structures on the scale of the pool diameter in pool Hires. Thus, air engulfment and visible flame structure are resolved. Manifolds for the gas-phase chemistry, soot formation, particle growth, soot diffusive/ thermophoretic transport are used to bridge the Batchelor and resolved (LES) scales

Studies on the electron transfer pathway, topography of iron-sulfur centers, and site of coupling in NADH-Q oxidoreductase.

Electron transfer activities and steady state reduction levels of Fe-S centers of NADH-Q oxidoreductase were measured in mitochondria, submitochondrial particles (ETPH), and complex I after treatment with various reagents. p-Chloromercuribenzenesulfonate destroyed the signal from center N-4 (gx = 1.88) in ETPH but not in mitochondria, showing that N-4 is accessible only from the matrix side of the inner membrane. N-Bromosuccinimide also destroyed the signal from N-4 but without inhibiting rotenone-sensitive electron transfer to quinone, suggesting a branched pathway for electron transfer. Diethylpyrocarbonate caused oxidation of N-3 and N-4 in the steady state without changing N-1, suggesting N-1 is before N-3 and N-4. Difluorodinitrobenzene and dicyclohexylcarbodiimide inhibited oxidation of all Fe-S centers and tetranitromethane inhibited reduction of all Fe-S centers. Titrations of the rate of superoxide (O2-) generation in rotenone-treated submitochondrial particles were similar with the ratio [NADH]/[NAD] and that of 3-acetyl pyridine adenine nucleotide in spite of different midpoint potentials of the two couples. On reaction with inhibitors the inhibition of O2- formation was similar to that of ferricyanide reductase rather than quinone reductase. The rate of O2- formation during ATP-driven reverse electron transfer was 16% of the rate observed with NADH. The presence of NAD increased the rate to 83%. The results suggest that bound, reduced nucleotide, probably E-NAD., is the main source of O2- in NADH dehydrogenase. The effect of ATP on the reduction levels of Fe-S centers in well-coupled ETPH was measured by equilibrating with either NADH/NAD or succinate/fumarate redox couples. With NADH/NAD none of the Fe-S centers showed ATP induced changes, but with succinate/fumarate all centers showed ATP-driven reduction with or without NAD present. The effect on N-2 was smaller than that on N-1, N-3, and N-4. These observations indicate that the major coupling interaction is between N-2 and the low potential centers, N-1, N-3, and N-4. Possible schemes of coupling in this segment are discussed

Solvent-exposed tryptophans probe the dynamics at protein surfaces

The dynamics of single tryptophan (W) side chain of protease subtilisin Carlsberg (SC) and myelin basic protein (MBP) were used for probing the surface of these proteins. The W side chains are exposed to the solvent, as shown by the extent of quenching of their fluorescence by KI. Time-resolved fluorescence anisotropy measurements showed that the rotational motion of W is completely unhindered in the case of SC and partially hindered in the case of MBP. The rotational correlation time (Φ) associated with the fast local motion of W did not scale linearly with the bulk solvent viscosity (η) in glycerol-water mixtures. In contrast, Φ values of either W side chains in the denatured proteins or the free W scaled almost linearly with η, as expected by the Stokes-Einstein relationship. These results were interpreted as indicating specific partitioning of water at the surface of the proteins in glycerol-water mixtures

Combined Lab-on-a-Chip and microarray approach for biomolecular interaction sensing using surface plasmon resonance imaging

Surface plasmon resonance imaging (SPR) is a well-established label-free detection technique for real-time biomolecular interaction measurements. An integrated LOC sensing system with fluidic control for sample movement to specific locations on microarray surface in combination with SPR imaging is demonstrated by the measurements of human IgG and anti-IgG interactions from 24 patterned regions.\u

Monitoring membrane protein conformational heterogeneity by fluorescence lifetime distribution analysis using the maximum entropy method

Due to the inherent difficulty in crystallizing membrane proteins, approaches based on fluorescence spectroscopy have proved useful in elucidating their conformational characteristics. The ion channel peptide gramicidin serves as an excellent prototype for monitoring membrane protein conformation and dynamics due to a number of reasons. We have analyzed conformational heterogeneity in membrane-bound gramicidin using fluorescence lifetime distribution analysis of tryptophan residues by the maximum entropy method (MEM). MEM represents a model-free and robust approach for analyzing fluorescence lifetime distribution. In this paper, we show for the first time, that fluorescence lifetime distribution analysis using MEM could be a convenient approach to monitor conformational heterogeneity in membrane-bound gramicidin in particular and membrane proteins in general. Lifetime distribution analysis by MEM therefore provides a novel window to monitor conformational transitions in membrane proteins

High-salt diet suppresses autoimmune demyelination by regulating the blood-brain barrier permeability

Sodium chloride, "salt," is an essential component of daily food and vitally contributes to the body's homeostasis. However, excessive salt intake has often been held responsible for numerous health risks associated with the cardiovascular system and kidney. Recent reports linked a high-salt diet (HSD) to the exacerbation of artificially induced central nervous system (CNS) autoimmune pathology through changes in microbiota and enhanced T(H)17 cell differentiation [M. Kleinewietfeld et al., Nature 496, 518-522 (2013); C. Wu et al., Nature 496, 513-517 (2013); N. Wilck et al., Nature 551, 585-589 (2017)]. However, there is no evidence that dietary salt promotes or worsens a spontaneous autoimmune disease. Here we show that HSD suppresses autoimmune disease development in a mouse model of spontaneous CNS autoimmunity. We found that HSD consumption increased the circulating serum levels of the glucocorticoid hormone corticosterone. Corticosterone enhanced the expression of tight junction molecules on the brain endothelial cells and promoted the tightening of the blood-brain barrier (BBB) thereby controlling the entry of inflammatory T cells into the CNS. Our results demonstrate the multifaceted and potentially beneficial effects of moderately increased salt consumption in CNS autoimmunity.We thank the Mass Spectrometry and NGS Core Facilities at the Max Planck Institute of Biochemistry for performing sample analysis for proteomics and mRNA-seq experiments