Stationary edge flames in a wedge with hydrodynamic variable-density interaction

Edge flames are a canonical two-dimensional flame structure appearing in more complicated combustion problems, such as lifted jet flames and in the dynamics of the growth and repair of flame holes in nonpremixed turbulent combustion. Typical theoretical configurations to study edge flames are unable to evaluate retreating edge flames with strong hydrodynamic-coupling. A new computational configuration is introduced which places the edge flame in a wedge-shaped counterflow with a mass sink, providing control over the position of the edge flame, and allowing access to stationary, hydrodynamically-coupled retreating flames (at high strain). This framework is first used to evaluate edge flames using a simple global one-step chemistry model and Fickian transport. This simple model is used to characterize the behavior of the resulting edge flames, including the relationship between flame speed and transverse strain rate and response to Lewis number variations. The details of the computational method will be discussed, including the underlying finite element method, the generation of boundary data, and the continuation of the flame through regions of varying transverse strain. This configuration is then applied to detailed ethylene-air combustion using a skeletal reduction of the USC Mech II combustion reaction model and a detailed transport model. The details of the ethylene-air edge flame are discussed, and comparisons are made between stoichiometric, fuel-lean, and fuel-rich compositions. Novel results characterizing the dilatation and vorticity near the flame front are provided, data which are necessary for the construction of potential flow approximations of hydrodynamically-coupled edge flames

Spirality: A Novel Way to Measure Spiral Arm Pitch Angle

We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 minutes per galaxy, assuming at least 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code's results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality's error bars overlapped 2DFFT's error bars for 26 of the 30 galaxies. The two methods' agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies' spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. The code package is freely available online; see Comments for URL.Comment: 19 pages, 9 figures, 3 tables. The code package is available at http://dafix.uark.edu/~doug/SpiralityCode

More development - more migration? The "migration hump" and its significance for development policy co-operation with sub-Saharan Africa

German and European efforts to reduce irregular migration, particularly from sub-Saharan Africa, place a great emphasis on development co-operation. The aim is for this to eliminate as many causes of such migration as possible. This raises questions concerning the interrelation of development and migration. In the academic debate, it is well established that socio-economic development promotes migration rather than reducing it. But this causal relationship is not as clear-cut as the corresponding "migration hump" model suggests. It is evident that migration decisions are also in-fluenced by further factors. It is therefore problematic when policy makers use this apparent evidence to assume stopping development aid will stop migration. The con-text of migration and development needs to be analysed with an eye towards managing multiple drivers of migration. Donor countries should also utilize development policy approaches that lead to co-operation with African partner states. (author's abstract

Do the students' preferred pedagogy relate to their ethnicity?

An increasing number of international students, whose culture of teaching and learning practices are very different from UK students, are studying at British universities. This study investigates multicultural students’ preferences using two different teaching approaches in the 2009/2010 academic year, which is explained in the framework of this study. The study sample was two groups, a total of 34 students who were studying Japanese as a non-credited module. Quantitative and qualitative data was collected using questionnaires. The results showed that students’ preferences in teaching and learning appeared to be altered and influenced by the British educational culture regardless of students’ previous educational culture. In addition, the sample participants’ preference of teaching and learning are categorised into three types based on the framework of the study. Those who are in the teaching profession in a multicultural learning environment are encouraged to take consideration of students’ previous educational culture. It is suggested to incorporate teaching and learning practices from non-Anglophone countries to the Anglophone originated teaching approach to capture different preferences of multicultural students, reflecting global international characteristics of teaching and learning environments

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas phase electronic structure and vibrational frequency calculations. These quantities are valid for those atmospheric clusters whose geometries correspond to a minimum on their potential energy surfaces. The Gibbs free energy of the minimum energy structure can be used to predict atmospheric concentrations of the cluster under a variety of conditions such as temperature and pressure. We present a computationally inexpensive procedure built on a genetic algorithm-based configurational sampling followed by a series of increasingly accurate screening calculations. The procedure starts by generating and evolving the geometries of a large set of configurations using semi-empirical models then refines the resulting unique structures at a series of high-level ab initio levels of theory. Finally, thermodynamic corrections are computed for the resulting set of minimum-energy structures and used to compute the Gibbs free energies of formation, equilibrium constants, and atmospheric concentrations. We present the application of this procedure to the study of hydrated glycine clusters under ambient conditions

Computation of Atmospheric Concentrations of Molecular Clusters from \u3cem\u3eab initio\u3c/em\u3e Thermochemistry

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas phase electronic structure and vibrational frequency calculations. These quantities are valid for those atmospheric clusters whose geometries correspond to a minimum on their potential energy surfaces. The Gibbs free energy of the minimum energy structure can be used to predict atmospheric concentrations of the cluster under a variety of conditions such as temperature and pressure. We present a computationally inexpensive procedure built on a genetic algorithm-based configurational sampling followed by a series of increasingly accurate screening calculations. The procedure starts by generating and evolving the geometries of a large set of configurations using semi-empirical models then refines the resulting unique structures at a series of high-level ab initio levels of theory. Finally, thermodynamic corrections are computed for the resulting set of minimum-energy structures and used to compute the Gibbs free energies of formation, equilibrium constants, and atmospheric concentrations. We present the application of this procedure to the study of hydrated glycine clusters under ambient conditions

Tectonic controls on the long-term carbon isotope mass balance

The long-term, steady-state marine carbon isotope record reflects changes to the proportional burial rate of organic carbon relative to total carbon on a global scale. For this reason, times of high δ¹³C are conventionally interpreted to be oxygenation events caused by excess organic burial. Here we show that the carbon isotope mass balance is also significantly affected by tectonic uplift and erosion via changes to the inorganic carbon cycle that are independent of changes to the isotopic composition of carbon input. This view is supported by inverse co-variance between δ¹³C and a range of uplift proxies, including seawater⁸⁷Sr/⁸⁶Sr, that demonstrates how erosional forcing of carbonate weathering outweighs that of organic burial on geological time scales. A model of the long-term carbon cycle shows that increases in δ¹³C need not be associated with increased organic burial and that alternative tectonic drivers (erosion, outgassing) provide testable and plausible explanations for sustained deviations from the long-term δ¹³C mean. Our approach emphasizes the commonly overlooked difference between how net and gross carbon fluxes affect the long-term carbon isotope mass balance, and may lead to reassessment of the role that the δ¹³C record plays in reconstructing the oxygenation of Earth’s surface environment