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The burning rate, surface temperature, drag, and extinction conditions of a single char particle moving in a gas are computed numerically. The effects of the size and velocity of the particle and of the temperature and composition of the gas are examined in the framework of a simple model that includes O2 and CO2 heterogeneous reactions and, in some cases, a diffusion-controlled CO oxidation flame in the gas around the particle. In agreement with known results, the burning rate is found to increase with the velocity of the particle when the Reynolds number of the gas flow ceases to be small. The temperature of the particle increases with the temperature and oxygen mass fraction of the gas and is little affected by the size and velocity of the particle, except in the vicinity of extinction. The drag coefficient is a decreasing function of the particle size and velocity in the range of Reynolds numbers that has been analyzed. The presence of CO2 in the gas may have an important effect on the gasification of small particles.

Usamos el método de Dinámica Molecular (DM) para obtener una descripción atomística de los procesos de difusión y estructura del aluminio líquido en un ámplio rango de temperaturas (900K - 2600K). En el estudio se utilizó un potencial de interacción por oscilante de largo alcance. La solución numérica de las ecuaciones de movimiento se llevó acabo mediante el algoritmo de Verlet. La simulación computacional se realizó sobre un sistema de 256 partículas, aplicando condiciones de frontera periódicas con el fin de reducir los efectos de superficie. El análisis de las funciones de distribución obtenidas muestran que la ordenación local se mantiene hasta altas temperaturas. La forma y altura de los picos en las funciones de correlación par varían significativamente con la temperatura, lo cual evidencia las peculiaridades de la variación de la estructura del líquido. Establecemos que el radio de correlación disminuye desde 0,9 hasta 0,4 nm en el intervalo de temperaturas estudiado, mientras que el primer número de coordinación varía desde 12 hasta 8,5 aproximadamente. El coeficiente de autodifusion del aluminio, determinado mediante el desplazamiento cuadrático medio de las partículas, se encuentra en concordancia con los datos experimentales., We use the classical molecular dynamics method (MD) to obtain an atomistic description of the diffusion and the structure of liquid aluminum in a wide range of temperatures (900 K - 2600 K). These studies use two-body long range oscillatory potentials. The numeric resolution of the motion equations is carried out by means of the Verlet algorithm. The MD simulation has been performed on a system of 256 particles using that short range order remains up to high temperatures. The height and shape of peaks suffer significant changes with the temperature, which evidences the peculiarities of changes in the liquid structure. The correlation radius decreases from 0,9 nm to 0,4 nm in the range of temperatures studied. We found that the first coordination number changes approximately in the interval of 12 - 8..5. The results of the measurements of the selfdiffusion coefficient in aluminum, carried out by means of the mean-squared displacement of the ions, are in agreement with experimental data.

We compute the ratio between the direct and the resolved photon components of single jet and dijet production in $ep$ collisions for the kinematical range covered by the most recent ZEUS data. We analyse the phenomenological consequences of different models for the structure of virtual photons in these observables and compare them with the available data. We also comment on the correlation between the so called $x_{\gamma}^{obs}$ and the `true' $x_{\gamma}$, that can be inferred from the data., Comment: epsfig, 5 figures