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Abstract: Lean premixed hydrogen flames are thermodiffusively unstable and burn in cellular structures. Within these cellular structures the flame is locally enriched by preferential diffusion of hydrogen, leading to local hotspots that burn more intensely than an idealized flat steady flame at comparable inlet conditions. We investigate the impact of this local enrichment on the formation of nitrogen oxides. We consider a two dimensional configuration in which lean premixed hydrogen–air flames interact with a weakly turbulent velocity field for a range of equivalence ratios. The simulations show that although peak temperatures remain well below 1800K (where thermal NO x traditionally is thought to become significant), these localized hot spots lead to significant production of nitric oxides, and the relative enhancement becomes increasingly significant with lower fuel equivalence ratios. A detailed examination of the reaction chemistry in these unsteady flames shows that at richer conditions the predominant path taken to convert nitrogen gas to nitric oxide is via NNH. For leaner flames a path through nitrous oxide becomes increasingly important. [ABSTRACT FROM AUTHOR]

Abstract: Simulations are routinely used to study the process of carbon dioxide (CO2) sequestration in saline aquifers. In this paper, we describe the modeling and simulation of the dissolution–diffusion–convection process based on a total velocity splitting formulation for a variable-density incompressible single-phase model. A second-order accurate sequential algorithm, implemented within a block-structured adaptive mesh refinement (AMR) framework, is used to perform high-resolution studies of the process. We study both the short-term and long-term behaviors of the process. It is found that the onset time of convection follows closely the prediction of linear stability analysis. In addition, the CO2 flux at the top boundary, which gives the rate at which CO2 gas dissolves into a negatively buoyant aqueous phase, will reach a stabilized state at the space and time scales we are interested in. This flux is found to be proportional to permeability, and independent of porosity and effective diffusivity, indicative of a convection-dominated flow. A 3D simulation further shows that the added degrees of freedom shorten the onset time and increase the magnitude of the stabilized CO2 flux by about 25%. Finally, our results are found to be comparable to results obtained from TOUGH2-MP. [Copyright &y& Elsevier]

This paper presents topology-based methods to robustly extract, analyze, and track features defined as subsets of isosurfaces. First, we demonstrate how features identified by thresholding isosurfaces can be defined in terms of the Morse complex. Second, we present a specialized hierarchy that encodes the feature segmentation independent of the threshold while still providing a flexible multiresolution representation. Third, for a given parameter selection, we create detailed tracking graphs representing the complete evolution of all features in a combustion simulation over several hundred time steps. Finally, we discuss a user interface that correlates the tracking information with interactive rendering of the segmented isosurfaces enabling an in-depth analysis of the temporal behavior. We demonstrate our approach by analyzing three numerical simulations of lean hydrogen flames subject to different levels of turbulence. Due to their unstable nature, lean flames burn in cells separated by locally extinguished regions. The number, area, and evolution over time of these cells provide important insights into the impact of turbulence on the combustion process. Utilizing the hierarchy, we can perform an extensive parameter study without reprocessing the data for each set of parameters. The resulting statistics enable scientists to select appropriate parameters and provide insight into the sensitivity of the results with respect to the choice of parameters. Our method allows for the first time to quantitatively correlate the turbulence of the burning process with the distribution of burning regions, properly segmented and selected. In particular, our analysis shows that counterintuitively stronger turbulence leads to larger cell structures, which burn more intensely than expected. This behavior suggests that flames could be stabilized under much leaner conditions than previously anticipated. [ABSTRACT FROM AUTHOR]

This paper introduces an adaptive mesh and algorithm refinement method for fluctuating hydrodynamics. This particle-continuum hybrid simulates the dynamics of a compressible fluid with thermal fluctuations. The particle algorithm is direct simulation Monte Carlo (DSMC), a molecular-level scheme based on the Boltzmann equation. The continuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS) equations, which incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. It uses a recently developed solver for the LLNS equations based on third-order Runge-Kutta. We present numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate dynamic adaptive refinement by the computation of a moving shock wave. Mean system behavior and second moment statistics of our simulations match theoretical values and benchmarks well. We find that particular attention should be paid to the spectrum of the flux at the interface between the particle and continuum methods, specifically for the nonhydrodynamic (kinetic) time scales. [ABSTRACT FROM AUTHOR]

Additionalvein (Adv) is a dominant mutation that affects the first wing vein in Drosophila. It also manifests a recessive lethal phenotype and is associated with a large inversion. Using a combination of genetic and cytogenetic techniques, we show that Adv interacts with engrailed (en), likely because one of the inversion breakpoints interferes with en function. Genetic interaction studies reveal that Adv is lethal in trans with various lethal alleles of en and gives an engrailed-like wing phenotype with weak alleles of en. In situ hybridization to polytene chromosomes using en cDNA demonstrates that one of the inversion breakpoints lies within the en coding region. Although the cause of the wing phenotype is not determined herein, it likely is caused by the other inversion breakpoint interfering with a different function. The characterization of this mutation could expedite studies to understand what molecular events result in the Adv phenotype and thereby provide insight into the development of the first wing vein in Drosophila.Key words: wing vein, dominant mutation, engrailed.L'allèle Additionalvein (Adv) est une mutation dominante qui affecte la première veine de l'aile chez le Drosophila. Elle entraîne également une létalité récessive et est associée à une grande inversion. En combinant des techniques génétiques et cytogénétiques, les auteurs montrent que Adv interagit avec engrailed (en), vraisemblablement parce que l'une des bornes de l'inversion interfère avec la fonction de en. Des études génétiques de l'interaction ont révélé que Adv est létale en trans avec plusieurs allèles létaux de en et produit un phénotype ressemblant à celui de en lorsque combiné avec des allèles faibles de en. Des hybridations in situ avec l'ADNc de en sur les chromosomes polytènes ont permis de démontrer que l'une des bornes de l'inversion est située au sein de la région codante de en. Bien que la cause de la modification phénotypique n'ait pas été élucidée par suite de ces travaux, ce phénotype résulte vraisemblablement de l'interférence de l'autre borne de l'inversion avec une fonction différente. La caractérisation de cette mutation pourrait faire avancer plus rapidement notre compréhension des événements qui produisent le phénotype Adv et, par le fait même, nous éclairer sur le développement de la première veine de l'aile chez le Drosophila.Mots clés : veine de l'aile, mutation dominante, engrailed.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

In Drosophila melanogaster, aeroplane (ae) is a regulatory allele of teashirt (tsh), and the mutant wing posture phenotype of homozygous ae flies is caused by a defect in the hinge region of the wing, whereby the base of the wing at the proximal ventral radius is fused to the thorax in the region of the pleural wing process. The apparent paralysis of the wings and the drooping halteres are caused by an I-element insertion into a 3' noncoding sequence of tsh. The cis-acting regulatory element interrupted by the I element is required, to drive tsh expression in the regions of the developing adult that give rise to proximal wing and haltere tissues. Loss of this expression results in the fusion of the proximal structures of the wing and halteres to the thoracic cuticle. Further characterization of this tsh regulatory motif has now identified an additional enhancer activity directing tsh expression in tissues forming portions of the midgut. Subdivision of this midgut enhancer activity has identified putative negatively acting motifs.Key words: Drosophila melanogaster, enhancer, development, wing posture, I element, teashirt, wing hinge, tissue-specificity.Chez le Drosophila melanogaster, aeroplane (ae) est un allèle à régulation altérée du gène teashirt (tsh). Le phénotype mutant de posture des ailes, observé chez les mouches homozygotes pour ae, est dû à un defaut dans la region posterieure de l'aile où la base de l'aile du radius proximal ventral est fusionnée au thorax dans la region du developpement de l'aile pleurale. L'apparente paralysie des ailes et l'apparence pendante des haltères sont causées par l'insertion d'un élément I dans la région 3' non-codante du gène tsh. L'élément cis interrompu par l'insertion de l'élément I dirige l'expression de tsh dans les régions de l'adulte en développement qui produisent les tissus de l'aile proximale et de l'haltère. La perte d'expression entraîne la fusion des structures proximales de l'aile et des haltères à la cuticule thoracique. Une plus ample caractérisation de cet élément cis du gène tsh a permis d'identifier une autre fonction activatrice dirigeant l'expression de tsh dans les tissus qui formeront des portions de l'intestin moyen. Une subdivision de cette fonction activatrice de l'expression dans l'intestin moyen a permis d'identifier des motifs putatifs impliqués dans un contrôle négatif.Mots clés : Drosophila melanogaster, activateur, développement, posture des ailes, élément I, teashirt, charnière de l'aile, spécificité tissulaire.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Dissociative adsorption onto a surface introduces dynamic correlations between neighboring sites not found in non-dissociative absorption. We study surface coverage dynamics where reversible dissociative adsorption of dimers occurs on a finite linear lattice. We derive analytic expressions for the equilibrium surface coverage as a function of the number of reactive sites, N, and the ratio of the adsorption and desorption rates. Using these results, we characterize the finite size effect on the equilibrium surface coverage. For comparable N's, the finite size effect is significantly larger when N is even than when N is odd. Moreover, as N increases, the size effect decays more slowly in the even case than in the odd case. The finite-size effect becomes significant when adsorption and desorption rates are considerably different. These finite-size effects are related to the number of accessible configurations in a finite system where the odd-even dependence arises from the limited number of accessible configurations in the even case. We confirm our analytical results with kinetic Monte Carlo simulations. We also analyze the surface-diffusion case where adsorbed atoms can hop into neighboring sites. As expected, the odd-even dependence disappears because more configurations are accessible in the even case due to surface diffusion. [ABSTRACT FROM AUTHOR]