Nonlinear cellular instabilities of planar premixed flames: numerical simulations of the Reactive Navier-Stokes equations

Two-dimensional compressible Reactive Navier-Stokes numerical simulations of intrinsic planar, premixed flame instabilities are performed. The initial growth of a sinusoidally perturbed planar flame is first compared with the predictions of a recent exact linear stability analysis, and it is shown the analysis provides a necessary but not sufficient test problem for validating numerical schemes intended for flame simulations. The long-time nonlinear evolution up to the final nonlinear stationary cellular flame is then examined for numerical domains of increasing width. It is shown that for routinely computationally affordable domain widths, the evolution and final state is, in general, entirely dependent on the width of the domain and choice of numerical boundary conditions. It is also shown that the linear analysis has no relevance to the final nonlinear cell size. When both hydrodynamic and thermal-diffusive effects are important, the evolution consists of a number of symmetry breaking cell splitting and re-merging processes which results in a stationary state of a single very asymmetric cell in the domain, a flame shape which is not predicted by weakly nonlinear evolution equations. Resolution studies are performed and it is found that lower numerical resolutions, typical of those used in previous works, do not give even the qualitatively correct solution in wide domains. We also show that the long-time evolution, including whether or not a stationary state is ever achieved, depends on the choice of the numerical boundary conditions at the inflow and outflow boundaries, and on the numerical domain length and flame Mach number for the types of boundary conditions used in some previous works

Exploring the Structure of Distant Galaxies with Adaptive Optics on the Keck-II Telescope

We report on the first observation of cosmologically distant field galaxies with an high order Adaptive Optics (AO) system on an 8-10 meter class telescope. Two galaxies were observed at 1.6 microns at an angular resolution as high as 50 milliarcsec using the AO system on the Keck-II telescope. Radial profiles of both objects are consistent with those of local spiral galaxies and are decomposed into a classic exponential disk and a central bulge. A star-forming cluster or companion galaxy as well as a compact core are detected in one of the galaxies at a redshift of 0.37+/-0.05. We discuss possible explanations for the core including a small bulge, a nuclear starburst, or an active nucleus. The same galaxy shows a peak disk surface brightness that is brighter than local disks of comparable size. These observations demonstrate the power of AO to reveal details of the morphology of distant faint galaxies and to explore galaxy evolution.Comment: 5 pages, Latex, 3 figures. Accepted for publication in P.A.S.

Lift-Off Characteristics and Flame Base Structure of Coal Seeded Gas Jet Flames

An experimental study of the burner rim stability characteristics and the flame base structure of flames co-fired with pulverized coal and propane gas is presented. Lift-off and reattachment characteristics are examined as functions of propane concentration in the jet stream for lignite, bituminous and anthracite coals. The effects on flame base structure are studied in terms of temperature, product species concentration and radiation profiles. The addition of lignite and anthracite coals favours the lift-off transitions. Bituminous coal, on the other hand, makes the flame more stable. The peak values of temperature and concentrations of major combustion product species in the flame stabilization region strongly depend upon the rank of coal. Among the coals tested, bituminous coal produces the highest peak temperature and its flame emits maximum radiation from the stabilization region. Anthracite and lignite coals produce somewhat comparable stability characteristics and structure of the flame base. The effects of coal rank are explained by the differences in volatile matter, moisture and pyrolysis characteristics of coals.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Classical generalized constant coupling model for geometrically frustrated antiferromagnets

A generalized constant coupling approximation for classical geometrically frustrated antiferromagnets is presented. Starting from a frustrated unit we introduce the interactions with the surrounding units in terms of an internal effective field which is fixed by a self consistency condition. Results for the magnetic susceptibility and specific heat are compared with Monte Carlo data for the classical Heisenberg model for the pyrochlore and kagome lattices. The predictions for the susceptibility are found to be essentially exact, and the corresponding predictions for the specific heat are found to be in very good agreement with the Monte Carlo results.Comment: 4 pages, 3 figures, 2 columns. Discussion about the zero T value of the pyrochlore specific heat correcte

Identification of publicly available data sources to inform the conduct of Health Technology Assessment in India

Background: Health technology assessment (HTA) provides a globally-accepted and structured approach to synthesising evidence for cost and clinical effectiveness alongside ethical and equity considerations to inform evidence-based priorities. India is one of the most recent countries to formally commit to institutionalising HTA as an integral component of the heath resource allocation decision-making process. The effective conduct of HTA depends on the availability of reliable data. Methods: We draw from our experience of collecting, synthesizing, and analysing health-related datasets in India and internationally, to highlight the complex requirements for undertaking HTA, and explore the availability of such data in India. We first outlined each of the core data components required for the conduct of HTA, and their availability in India, drawing attention to where data can be accessed, and different ways in which researchers can overcome the challenges of missing or low quality data. Results: We grouped data into the following categories: clinical efficacy; cost; epidemiology; quality of life; service use/consumption; and equity. We identified numerous large local data sources containing epidemiological information. There was a marked absence of other locally-collected data necessary for informing HTA, particularly data relating to cost, service use, and quality of life. Conclusions: The introduction of HTA into the health policy space in India provides an opportunity to comprehensively assess the availability and quality of health data capture across the country. While epidemiological information is routinely collected across India, other data inputs necessary for HTA are not readily available. This poses a significant bottleneck to the efficient generation and deployment of HTA into the health decision space. Overcoming these data gaps by strengthening the routine collection of comprehensive and verifiable health data will have important implications not only for embedding economic analyses into the priority setting process, but for strengthening the health system as a whole

Strengthening health technology assessment systems in the global south: a comparative analysis of the HTA journeys of China, India and South Africa.

BACKGROUND: Resource allocation in health is universally challenging, but especially so in resource-constrained contexts in the Global South. Pursuing a strategy of evidence-based decision-making and using tools such as Health Technology Assessment (HTA), can help address issues relating to both affordability and equity when allocating resources. Three BRICS and Global South countries, China, India and South Africa have committed to strengthening HTA capacity and developing their domestic HTA systems, with the goal of getting evidence translated into policy. Through assessing and comparing the HTA journey of each country it may be possible to identify common problems and shareable insights. OBJECTIVES: This collaborative paper aimed to share knowledge on strengthening HTA systems to enable enhanced evidence-based decision-making in the Global South by: Identifying common barriers and enablers in three BRICS countries in the Global South; and Exploring how South-South collaboration can strengthen HTA capacity and utilisation for better healthcare decision-making. METHODS: A descriptive and explorative comparative analysis was conducted comprising a Within-Case analysis to produce a narrative of the HTA journey in each country and an Across-Case analysis to explore both knowledge that could be shared and any potential knowledge gaps. RESULTS: Analyses revealed that China, India and South Africa share many barriers to strengthening and developing HTA systems such as: (1) Minimal HTA expertise; (2) Weak health data infrastructure; (3) Rising healthcare costs; (4) Fragmented healthcare systems; and (5) Significant growth in non-communicable diseases. Stakeholder engagement and institutionalisation of HTA were identified as two conducive factors for strengthening HTA systems. CONCLUSION: China, India and South Africa have all committed to establishing robust HTA systems to inform evidence-based priority setting and have experienced similar challenges. Engagement among countries of the Global South can provide a supportive platform to share knowledge that is more applicable and pragmatic