A wildland fire is a complex, multi-scale, and multi-process dynamical system with its instantaneous state depending on chemical and physical processes occurring on a hierarchy of spatial and temporal scales. Observations of multiscale processes affecting the wildland fire are very difficult to make. These scales are as small as fuel particles during the combustion process (order of <10 cm), flame structures and heat transfer (order of one to tens of meters), and microscale/mesoscale meteorological processes (orders of 10-10 000 m) (Morvan, 2011;Sullivan, 2017aSullivan, , 2017b. As point measurements, micrometeorological in situ towers in experimental burns provide spatially limited information over a brief period of time as the fire approaches and then travels underneath the instrumented tower (
In pyrometallurgical processes refining copper, the main source of loss in the conversion stage is from slag. This paper reports on research work treating converter slag containing high percentages of copper (36 wt%) using ammonium hydroxide at room temperature. Variables analyzed are solution pH, agitation, temperature, NH4OH concentration and particle size. Results showed that the hydronium ion resulting from ammonium hydroxide dissociation was the main oxidant of copper compounds in slag, such as CuO, Cu2O and Cu, with the exception of CuFeO2. The particles contain a large amount of microcracks (porosity) in their refractory structure (analyzed by compositional image capture (BSE)). Thus, the diffusion of the leaching solution through the microcracks making contact with the copper oxides would be allowed. Leaching mechanisms were corroborated by X-ray diffraction and scanning electron microscopy analysis. Increasing temperature and NH4OH concentration while decreasing particle size obtained higher copper recoveries, reaching values of 84.8%. Under the same conditions, the main impurity (iron) was minimal (<2%). Solution pH also affected slag leaching. Agitation of the solution positively affected the rate of copper extraction. Leaching kinetics of the leaching solution through the porosity formed in the slag was analyzed under the intraparticle diffusion model. The reaction order was 1.2 with respect to the concentration of ammonium hydroxide and the model was inversely proportional to the square of the particle radius. The activation energy obtained was 42.3 kJ/mol for temperature range 283 to 333 K.
Background. Wildfires propagate through vegetation exhibiting complex spread patterns modulated by ambient atmospheric wind turbulence. Wind gusts at the fire-front extend and intensify flames causing direct convective heating towards unburnt fuels resulting in rapid acceleration of spread. Aims. To characterise ambient and fire turbulence over gorse shrub and explore how this contributes to fire behaviour. Methods. Six experimental burns were carried out in Rakaia, New Zealand under varying meteorological conditions. The ignition process ensured a fire-line propagating through dense gorse bush (1 m high). Two 30-m sonic anemometer towers measured turbulent wind velocity at six different levels above the ground. Visible imagery was captured by cameras mounted on uncrewed aerial vehicles at 200 m AGL. Key results. Using wavelet decomposition, we identified different turbulent time scales that varied between 1 and 128 s relative to height above vegetation. Quadrant analysis identified statistical distributions of atmospheric sweeps (downbursts of turbulence towards vegetation) with sustained events emanating from above the vegetation canopy and impinging at the surface with time scales up to 10 s. Conclusions. Image velocimetry enabled tracking of 'fire sweeps' and characterised for the first time their lifetime and dynamics in comparison with overlying atmospheric turbulent structures. Implications. This methodology can provide a comprehensive toolkit when investigating coupled atmosphere-fire interactions.
Este articulo presenta algunas metodologias para cuantificar riesgo cuando la distribucion de perdidas presenta eventos extremos, debido a que los activos financieros generalmente presentan alta curtosis. De esta manera, el principal concepto utilizado en el documento es el valor en riesgo (VaR, por sus siglas en ingles), medida introducida por J. P. Morgan en 1995. Desde el punto de vista estadistico, VaR es un cuantil de una funcion de distribucion; sin embargo, su valor dependera de la forma de la distribucion que se utilice para ajustar los datos de perdida. Por tal razon, al estimar de manera confiable el parametro de forma de la distribucion de perdidas, se obtiene un estimador confiable de medida de riesgo. La teoria del valor extremo (EVT, por sus siglas en ingles) es una tecnica estadistica que ha sido empleada para tal fin. En este documento se utiliza la metodologia de EVT, denominada picos sobre el umbral (POT, por sus siglas en ingles), en el cual, se estima el parametro de forma de la distribucion de excesos mediante maxima verosimilitud. Este metodo de estimacion se revisa brevemente en el documento junto con el metodo de minimos cuadrados ponderados. Este ultimo se utiliza para cuantificar el estimador de Hill y con este valor se calcula el VaR para distribuciones con colas pesadas. Finalmente, se comparan las metodologias propuestas en el articulo para cuantificar VaR con otras dos metodologias que son simulacion historica y bajo el supuesto de normalidad mediante pruebas de desempeno a dos casos.
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