Application of the Fernandez-Terrazo et al. one-step chemistry model for partially premixed combustion to n-heptane

A set of model parameters has been derived for the use of the model with n-heptane following the procedure set out by Fernandez et al

Analysis of turbulent flame propagation in equivalence ratio-stratified flow

Equivalence ratio-stratified combustion is an important technology for achieving stable low-emission operation in internal combustion engines and gas turbines. This study examines how equivalence ratio stratification affects the physics of turbulent flame propagation using Direct Numerical Simulation. Three-dimensional simulations of a turbulent slot-Bunsen flame configuration are performed with accurate multi-step kinetic modelling for methane-air combustion. We compare one perfectly-premixed and three equivalence ratio-stratified cases with the mean equivalence ratio gradient aligned with, tangential to or opposed to the mean flame brush. The simulation results are analysed in terms of flame surface area and the burning intensity. The local effects of stratification are then investigated further by examining statistics of the displacement speed conditioned on the flame-normal equivalence ratio gradient. The local burning intensity is found to depend on the orientation of the stratification with respect to the flame front, so that burning intensity is enhanced when the flame speed in the products is faster than in the reactants. This effect of alignment between equivalence ratio gradients and flame fronts has been observed previously in laminar flames and it is found here that it also affects the global behaviour of turbulent flames. The flame surface area is also influenced by equivalence ratio stratification and this may be explained by differences in the surface-averaged consumption speed and differential propagation effects due to flame speed variations associated with equivalence ratio fluctuations

Large eddy simulation of a lifted ethylene flame using a dynamic nonequilibrium model for subfilter scalar variance and dissipation rate

Accurate prediction of nonpremixed turbulent combustion using large eddy simulation(LES) requires detailed modeling of the mixing between fuel and oxidizer at scales finer than the LES filter resolution. In conserved scalar combustion models, the small scale mixing process is quantified by two parameters, the subfilter scalar variance and the subfilter scalar dissipation rate. The most commonly used models for these quantities assume a local equilibrium exists between production and dissipation of variance. Such an assumption has limited validity in realistic, technically relevant flow configurations. However, nonequilibrium models for variance and dissipation rate typically contain a model coefficient whose optimal value is unknown a priori for a given simulation. Furthermore, conventional dynamic procedures are not useful for estimating the value of this coefficient. In this work, an alternative dynamic procedure based on the transport equation for subfilter scalar variance is presented, along with a robust conditional averaging approach for evaluation of themodel coefficient. This dynamic nonequilibrium modeling approach is used for simulation of a turbulent lifted ethylene flame, previously studied using DNS by Yoo et al. (Proc. Comb. Inst., 2011). The predictions of the new model are compared to those of a static nonequilibrium modeling approach using an assumed model coefficient, as well as those of the equilibrium modeling approach. The equilibrium models are found to systematically underpredict both subfilter scalar variance and dissipation rate. Use of the dynamic procedure is shown to increase the accuracy of the nonequilibrium modeling approach. However, numerical errors that arise as a consequence of grid-based implicit filtering appear to degrade the accuracy of all three modeling options. Thus, while these results confirm the usefulness of the new dynamic model, they also show that the quality of subfilter model predictions depends on several factors extrinsic to the formulation of the subfilter model itself

Wolf (Canis lupus) Predation of a Polar Bear (Ursus maritimus) Cub on the Sea Ice off Northwestern Banks Island, Northwest Territories, Canada

We describe the apparent predation of a polar bear (Ursus maritimus) cub by wolves (Canis lupus) on the sea ice just off the northwest coast of Banks Island, Northwest Territories, Canada. On 20 April 2004, while following the tracks of a female bear and two cubs-of-the-year in the snow during a helicopter survey, we noted that the bear tracks had been joined by several sets of wolf tracks. After following both sets of tracks for about 1 km, we observed a disturbed area in the snow with numerous overlying tracks. Upon landing and searching the site, we found the remains of a polar bear cub that the wolves had successfully separated from its mother and killed. This is only the second documented observation ever made of a polar bear killed by wolves.Nous décrivons la prédation apparente d’un ourson polaire (Ursus maritimus) par des loups (Canis lupus) sur la glace marine, tout près de la côte nord-ouest de l’île Banks, dans les Territoires du Nord-Ouest, au Canada. Le 20 avril 2004, après avoir suivi les traces d’une ourse et de deux oursons de l’année dans la neige lors d’une inspection en hélicoptère, nous avons remarqué que les traces d’ours avaient été rejointes par plusieurs séries de traces de loups. Après avoir suivi les deux séries de traces sur environ un kilomètre, nous avons remarqué que la neige avait été dérangée et que les traces se recoupaient beaucoup. Nous avons atterri, fouillé l’emplacement et trouvé les restes d’un ourson polaire que les loups avaient réussi à séparer de sa mère pour le tuer. Il ne s’agit là que de la deuxième observation à n’avoir jamais été recensée à propos de loups ayant tué un ours polaire

Determinants of migrant career success: A study of recent skilled migrants in Australia

Australia has been aggressively pursuing skilled migrants to sustain its population and foster economic growth. However, many skilled migrants experience a downward career move upon migration to Australia. Based on a survey of recent skilled migrants, this study investigates how individual (age, years of settlement, qualifications), national/societal (citizenship and settlement), and organization‐level (climate of inclusion) factors influence their career success. Overall, we found that: (1) age at migration matters more than length of settlement in predicting skilled migrant career success; (2) citizenship uptake and living in a neighbourhood with a greater number of families from the same country of origin facilitate post‐migration career success; and (3) perceptions of one\u27s social/informal networks in the workplace – a dimension of perceived organizational climate of inclusion – also have a positive impact on migrant career outcomes

Assembly of the Inner Perivitelline Layer, a Homo log of the Mammalian Zona Pellucida: An Immunohistochemical and Ultrastructural Study

The avian inner perivitelline layer (IPVL), a homologous structure to the mammalian zona pellucida, is deposited between the granulosa cells and the oocyte cell membrane during folliculogenesis. The glycoprotein meshwork of the IPVL forms a 3-dimensional matrix and possesses important functions in the fertilization process: it contributes to the binding of avian spermatozoa to the oocyte and induces acrosomal exocytosis. In contrast to the zona pellucida of mammals, the IPVL does not prevent the physiological polyspermy found in birds. Previous studies have shown that in the Japanese quail (Cotumix japonica) at least 5 glycoproteins are constituents of the IPVL (ZP1, ZP2, ZP3, ZP4, and ZPD). In this study, we investigated the spatiotennporal assembly pattern of the IPVL during folliculogenesis using immunohistochemical and ultrastructural methods. The obtained results clearly show that these glycoproteins are incorporated into the IPVL at distinct points during follicular development, supporting the hypothesis that ZP2 and ZP4 form a type of prematrix into which ZP1, ZP3, and ZPD are integrated at a later stage of development. Copyright (C) 2011 S. Karger AG, Base

Canary in the coalmine: Norwegian attitudes towards climate change and extreme long-haul air travel to Aotearoa/New Zealand

Accelerating global climate change poses considerable challenges to all societies and economies. The European Union now targets a 20% reduction in CO2 emissions by 2020. Indeed, the Labour-led Norwegian government is committed to carbon neutrality across all sectors of the economy by 2030. Aviation has been identified as a rapidly growing contributor to CO2 emissions. This article reports on a research project that explored Norwegian attitudes towards climate change, particularly as they relate to extreme long-haul air travel to Aotearoa/New Zealand. It reveals that the 'dream trip' to New Zealand for Norwegians is still largely intact. It also finds evidence of 'air travel with a carbon conscience' arising from growing concern for high frequency discretionary air travel. Evidence of denial of the climate impact of air travel that recent studies have revealed was largely absent. Interviewees expressed a greater concern for short-haul air travel emissions than for the climate impact of long-haul travel. However, intentions to adapt long-haul travel behaviours were expressed, highlighting the need to monitor consumer attitudes towards the impact of air travel on climate change. We conclude that Norway is a vanguard European tourism market in terms of climate sensitivity

Optical properties of MgH2 measured in situ in a novel gas cell for ellipsometry/spectrophotometry

The dielectric properties of alpha-MgH2 are investigated in the photon energy range between 1 and 6.5 eV. For this purpose, a novel sample configuration and experimental setup are developed that allow both optical transmission and ellipsometric measurements of a transparent thin film in equilibrium with hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about 80% over the whole visible spectrum. The dielectric function found in this work confirms very recent band structure calculations using the GW approximation by Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a cap layer we report also the optical properties of PdHx thin films.Comment: REVTeX4, 15 pages, 12 figures, 5 table

Towards Machine Wald

The past century has seen a steady increase in the need of estimating and predicting complex systems and making (possibly critical) decisions with limited information. Although computers have made possible the numerical evaluation of sophisticated statistical models, these models are still designed \emph{by humans} because there is currently no known recipe or algorithm for dividing the design of a statistical model into a sequence of arithmetic operations. Indeed enabling computers to \emph{think} as \emph{humans} have the ability to do when faced with uncertainty is challenging in several major ways: (1) Finding optimal statistical models remains to be formulated as a well posed problem when information on the system of interest is incomplete and comes in the form of a complex combination of sample data, partial knowledge of constitutive relations and a limited description of the distribution of input random variables. (2) The space of admissible scenarios along with the space of relevant information, assumptions, and/or beliefs, tend to be infinite dimensional, whereas calculus on a computer is necessarily discrete and finite. With this purpose, this paper explores the foundations of a rigorous framework for the scientific computation of optimal statistical estimators/models and reviews their connections with Decision Theory, Machine Learning, Bayesian Inference, Stochastic Optimization, Robust Optimization, Optimal Uncertainty Quantification and Information Based Complexity.Comment: 37 page