Sand Particle Size Distribution Research Articles

Role of particle-size distributions on millimetre-wave propagation in sand/dust storms

Particle size distributions of sand and dust are surveyed. Various assumptions for the theoretical prediction of the effect of particles on MMW propagation are discussed and justified. A general formula of the propagation parameters, for any particle shape and any distribution, is developed. It is found that the MMW propagation depends strongly on the probability density function of particle size distribution. A simplelinear relationship is shown between ‘α, π’ and an ‘effective radius’ of the storm. Attenuation and phase shift due to spherical and ellipsoidal particles are calculated for four distributions, namely power law, exponential, lognormal and normal. Results are presented and the role of the distributions is discussed

Experimental particle size distributions and their representation by log—hyperbolic functions

Following previous studies by Bagnold and Barndorff-Nielsen et al., the present work employs the log—hyperbolic function to fit experimentally measured particle size distributions originating from quite different experiments. It is shown that the log—hyperbolic function permits a satisfactory representation of all size distributions studied in this work. Hence, it appears that experimental particle size distributions are well described by the four characteristic parameters occurring in the log—hyperbolic function. These parameters can therefore be employed to study similarities or differences between particle size distributions and/or to describe temporal and spatial variations of distributions. The function was applied to the following particle size distributions: 1. — Mass—size distribution of a sand sample 2. — Size distribution of diamonds 3. — Size distribution of river bed sediments 4. — Size distribution of glacio-fluvial sediments 5. — Measurements of aerosol distributions 6. — Particle size distributions in sprays 7. — Molecular weight distributions A brief account of previous work is given and the major properties of the log—hyperbolic function are described. Experimental particle size distributions of sand, diamonds, river bed sediments, spray droplets, aerosols, and polymer molecules are fitted by the log—hyperbolic function and it is shown that it satisfactorily applies to all distributions.

Effects of Sandstorms on Microwave Propagation

Low rainfull volume suggests the promise of long paths using higher microwave frequencies for radio communication in desert areas. The pursuit of this promise gives rise to the need for understanding the effects of sandstorms on microwave propagation. First, a distinction should be made between large sand grains and fine sand dust <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> Sand grains of greater than about O.2-mm diameter are driven by the wind as a low-flying cloud with a height of les than about 2 meters above the ground. This limited height is expected to be lower than most antenna heights of a microwave station. On the other hand, dust-like sand particles can rise in dense clouds to a height of one kilometer or more. This latter type of sandstorm, which is essentially a misnomer for dust storm, may lie in the terrestrial and earth-space paths of microwave radio; hence, path attenuation data are required. Precise calculation is hampered by the uncertainty about the dielectric constant and the size distribution of sand particles. However, useful analysis and frequency dependence of the sandstorm effects can be obtained without precise knowledge of these parameters.

Técnica para o estudo granulométrico da fração areia dos solos

Neste trabalho é apresentada uma técnica para o estudo granulométrico da fração areia, sua expressão numérica, representação gráfica e análise estatística. Foi feito um ensaio preliminar para verificar a partir de que tempo de peneiragem os resultados obtidos se mostravam reprodutíveis. Os tempos de 10, 20 e 30 minutos deram resultados pràticamente iguais, revelando também ser pequeno o erro devido a outros fatores. A aplicação do método de estudo à fração areia de solos provenientes dos arenitos Bauru e Botucatu, do planalto de São Carlos e da Serra de Santana, permitiu evidenciar uma diferença flagrante das distribuições granulométricas respectivas. O emprêgo da representação gráfica ressaltou o caráter dessas diferenças, confirmadas pelos resultados da análise estatística. O solo do arenito Botucatu apresenta uma distribuição mais regular, com menor amplitude. A amplitude cresce para os solos da Serra de Santana e planalto de São Carlos e para o arenito Bauru. Nesta última amostra a distribuição é mais regular que naquelas duas. Em relação à moda, os resultados acusam maior quantidade de fração grosseira nas amostras da Serra de Santana e do planalto de São Carlos, maior predominância de frações finas no arenito Bauru. No arenito Botucatu as duas frações estão mais próximas, predominando ainda a areia fina. Apesar das restrições da expressão dos resultados ponderais em freqüência numérica, o método revelou-se eficiente na comparação da distribuição granulométrica da fração areia de solos provenientes de diversas formações sedimentares.

PRELIMINARY NOTE ON THE GRANULOMETRIC ANALYSIS OF SEDIMENTARY ROCKS

The observation that the results of line and point counting analyses of the particle size distribution of the same sand are different leads to the conclusion that these results are biased by the sampling technique1. The influence of the currently used sampling techniques on the numerical results of a particle size analysis is discussed. Evidence is presented to show that the use of line and point counting methods in granulometric analysis leads to results in which the influence of the sampling method is so strong that the practical value of these techniques is doubtful. It is therefore considered advisable to discontinue line and point counting techniques in granulometric analysis in favour of ribbon sampling methods.