A numerical study of chemically reacting flow in nozzles

The space station uses small rocket motors, called thrusters, for orientation control. Because of the lack of viable design tools for small rockets, the initial thruster design was basically a very small version of a large rocket motor. Thrust measurements of the initial design were lower than predicted. To improve predictions it was decided to develop a verison of the RPLUS2D reacting flow code for thruster calculations. RPLUS2D employs an implicit finite volume, lower-upper symmetric successive overrelaxation (LU-SSOR) scheme for solving the complete two-dimensional Navier-Stokes equations and species transport equations in a coupled and very efficient manner. The combustion processes are modeled by a 9-species, 18 step finite-rate chemistry model, and the turbulence is simulated by a Baldwin-Lomax algebraic model. The code is extended to handle multiple subsonic inlet conditions where the total mass flow is governed by conditions calculated at the thruster-throat. Results are shown for a thruster design where the overall mixture ratio is hydrogen rich. A calculation of a large area ratio divergent nozzle is also presented

Manin's conjecture on a nonsingular quartic del Pezzo surface

Given a nonsingular quartic del Pezzo surface, a conjecture of Manin predicts the density of rational points on the open subset of the surface formed by deleting the lines. We prove that this prediction is of the correct order of magnitude for a particular surface.Comment: 29 page

Effects of droplet interactions on droplet transport at intermediate Reynolds numbers

Effects of droplet interactions on drag, evaporation, and combustion of a planar droplet array, oriented perpendicular to the approaching flow, are studied numerically. The three-dimensional Navier-Stokes equations, with variable thermophysical properties, are solved using finite-difference techniques. Parameters investigated include the droplet spacing, droplet Reynolds number, approaching stream oxygen concentration, and fuel type. Results are obtained for the Reynolds number range of 5 to 100, droplet spacing from 2 to 24 diameters, oxygen concentrations of 0.1 and 0.2, and methanol and n-butanol fuels. The calculations show that the gasification rates of interacting droplets decrease as the droplet spacings decrease. The reduction in gasification rates is significant only at small spacings and low Reynolds numbers. For the present array orientation, the effects of interactions on the gasification rates diminish rapidly for Reynolds numbers greater than 10 and spacings greater than 6 droplet diameters. The effects of adjacent droplets on drag are shown to be small

Prediction of the structure of fuel sprays in gas turbine combustors

The structure of fuel sprays in a combustion chamber is theoretically investigated using computer models of current interest. Three representative spray models are considered: (1) a locally homogeneous flow (LHF) model, which assumes infinitely fast interphase transport rates; (2) a deterministic separated flow (DSF) model, which considers finite rates of interphase transport but ignores effects of droplet/turbulence interactions; and (3) a stochastic separated flow (SSF) model, which considers droplet/turbulence interactions using random sampling for turbulence properties in conjunction with random-walk computations for droplet motion and transport. Two flow conditions are studied to investigate the influence of swirl on droplet life histories and the effects of droplet/turbulence interactions on flow properties. Comparison of computed results with the experimental data show that general features of the flow structure can be predicted with reasonable accuracy using the two separated flow models. In contrast, the LHF model overpredicts the rate of development of the flow. While the SSF model provides better agreement with measurements than the DSF model, definitive evaluation of the significance of droplet/turbulence interaction is not achieved due to uncertainties in the spray initial conditions

Numerical study of chemically reacting flows using an LU scheme

A new computational fluid dynamic code has been developed for the study of mixing and chemical reactions in the flow fields of ramjets and scramjets. The code employs an implicit finite volume, lower-upper symmetric successive overrelaxation scheme for solving the complete two-dimensional Navier-Stokes equations and species transport equations in a fully-coupled and very efficient manner. The combustion processes are modeled by an 8-species, 14-step finite rate chemistry model whereas turbulence is simulated by a Baldwin-Lomax algebraic model. The validity of the code is demonstrated by comparing the numerical calculations with both experimental data and previous calculations of a cold flow helium injection into a straight channel and premixed hydrogen-air reacting flows in a ramped duct. The code is then used to calculate the mixing and chemical reactions of a hydrogen jet transversely injected into a supersonic airstream. Results are presented describing the flow field, the recirculation regions in front and behind the injector, and the chemical reactions

Gut Community Response to Wheat Bran and Pinto Bean

There is general consensus among the scientific community that dietary fibers reduce the risk of Western diseases through their fermentation by beneficial microbial communities in the human gut. However, dietary fibers in wheat bran (WB) and pinto bean (PB) are incompletely fermented by the gut microbiota. Therefore, there is a critical need to identify gut microbial communities that can increase fermentation of dietary fibers from these foods to maximize their disease-preventing properties. The goal of this study was to identify such communities with increased capacity to ferment the dietary fibers in WB and PB. To accomplish these goals, a stepwise in vitro fecal fermentation strategy with a modification to select for WB- and PB-associated microbes was employed. Over the course of 96 h of fermentation, fecal microbiomes treated with WB either maintained or improved their carbohydrate utilization capability, while the carbohydrate utilization capability of fecal microbiomes treated with PB varied by microbiome. At the end of 96 h of fermentation, WB-associated microbiomes had higher relative abundances of Bifidobacterium, Bacteroides, Prevotella 9, Enterococcus, Agathobacter, Roseburia, Ruminococcus 1, Dialister, Mitsuokella, and Veillonella, while PB-associated microbiomes had higher Bifidobacterium, Bacteroides, Prevotella 9, Enterococcus, [Ruminococcus] gnavus group, [Ruminococcus] torques group, Agathobacter, Lachnospiraceae NK4A136 group, Roseburia, Dialister, Veillonella, and uncl_Enterobacteriaceae compared with a control containing only media. There were also other genera that were associated with WB or PB substrates, but varied by microbiome. Both WB- and PB-associated communities were propiogenic in nature. These findings are important in developing effective intervention strategies to help increase dietary fiber fermentation and reduce the risk of disease. Advisor: Devin J. Ros

Mobilising Without the Masses and Mainstreaming Women’s Rights: A Case Study of the Local Women’s Movement in Malaysia

This thesis offers a critical evaluation of the women’s movement in relation to the problem of violence against women in the local context of Malaysia. It provides an analysis of the key strategies employed by local women’s organisations to address various forms of violence against women, including coalition building, engagement with UN mechanisms and the use of the media. This thesis also discusses the challenges of patriarchal cultures and mind-sets facing the local women’s movement, as well as the culture of fear that is prevalent in the Malaysian society and highlights the ways in which local women’s organisations work within the constraints of a semi authoritarian state. In addition, this thesis offers a critical analysis of the language and frameworks adopted by the local women’s movement in order to address the issue of violence against women. More precisely, it examines the ways and extent in which local women’s organisations engage in the framework of feminism and the talk of rights. Overall, this thesis seeks to account for the nuances and complexities involved in local women organising and provide a better understanding of the dynamics of the women’s movement in Malaysia

Age-dependent decline in beta-cell proliferation restricts the capacity of beta-cell regeneration in mice.

ObjectiveThe aim of this study was to elucidate whether age plays a role in the expansion or regeneration of beta-cell mass.Research design and methodsWe analyzed the capacity of beta-cell expansion in 1.5- and 8-month-old mice in response to a high-fat diet, after short-term treatment with the glucagon-like peptide 1 (GLP-1) analog exendin-4, or after streptozotocin (STZ) administration.ResultsYoung mice responded to high-fat diet by increasing beta-cell mass and beta-cell proliferation and maintaining normoglycemia. Old mice, by contrast, did not display any increases in beta-cell mass or beta-cell proliferation in response to high-fat diet and became diabetic. To further assess the plasticity of beta-cell mass with respect to age, young and old mice were injected with a single dose of STZ, and beta-cell proliferation was analyzed to assess the regeneration of beta-cells. We observed a fourfold increase in beta-cell proliferation in young mice after STZ administration, whereas no changes in beta-cell proliferation were observed in older mice. The capacity to expand beta-cell mass in response to short-term treatment with the GLP-1 analog exendin-4 also declined with age. The ability of beta-cell mass to expand was correlated with higher levels of Bmi1, a polycomb group protein that is known to regulate the Ink4a locus, and decreased levels of p16(Ink4a)expression in the beta-cells. Young Bmi1(-/-) mice that prematurely upregulate p16(Ink4a)failed to expand beta-cell mass in response to exendin-4, indicating that p16(Ink4a)levels are a critical determinant of beta-cell mass expansion.Conclusionsbeta-Cell proliferation and the capacity of beta-cells to regenerate declines with age and is regulated by the Bmi1/p16(Ink4a)pathway

Predictions of spray combustion interactions

Mean and fluctuating phase velocities; mean particle mass flux; particle size; and mean gas-phase Reynolds stress, composition and temperature were measured in stationary, turbulent, axisymmetric, and flows which conform to the boundary layer approximations while having well-defined initial and boundary conditions in dilute particle-laden jets, nonevaporating sprays, and evaporating sprays injected into a still air environment. Three models of the processes, typical of current practice, were evaluated. The local homogeneous flow and deterministic separated flow models did not provide very satisfactory predictions over the present data base. In contrast, the stochastic separated flow model generally provided good predictions and appears to be an attractive approach for treating nonlinear interphase transport processes in turbulent flows containing particles (drops)