Product Of Grain Size Research Articles

Quantifying reef-derived sediment generation: Introducing the SedBudget methodology to support tropical coastline and island vulnerability studies

AbstractStandardised methodologies for assessing reef-derived sediment generation rates do not presently exist. This represents a major knowledge gap relevant to better predicting reef-derived shoreline sediment supply. The census-based SedBudget method introduced here generates estimates of sediment composition and grain-size production as a function of the abundance and productivity of the major sediment-generating taxa at a reef site. Initial application of the method to several reefs in the northern Chagos Archipelago, Indian Ocean, generated total sediment generation estimates ranging from (mean ± SE) 0.7 ± 0.1 to 4.3 ± 1.3 kg CaCO3m−2 yr−1. Sediment production was dominated by parrotfishes (>90% at most sites), with site-variable secondary contributions from sea urchins (up to 20%), endolithic sponges (~1–7%) and benthic foraminifera (~0.5–3.5%). These taxa-level contributions are predicted to generate sediments that at all sites are coral- (83–94%) and crustose coralline algae-dominated (range ~ 5–12%). Comparisons between these estimates and sedimentary data from proximal reef and island beach samples generally show a high degree of consistency, suggesting promise in the SedBudget approach. We conclude by outlining areas where additional datasets and revised methodologies are most needed to improve rate estimates and hope that the methodology will stimulate research on questions around sediment production, transport and shoreline maintenance.

Combined effects of grain size, flow volume and channel width on geophysical flow mobility: three-dimensional discrete element modeling of dry and dense flows of angular rock fragments

Abstract. We have carried out new three-dimensional numerical simulations by using a discrete element method (DEM) to study the mobility of dry granular flows of angular rock fragments. These simulations are relevant for geophysical flows such as rock avalanches and pyroclastic flows. The model is validated by previous laboratory experiments. We confirm that (1) the finer the grain size, the larger the mobility of the center of mass of granular flows; (2) the smaller the flow volume, the larger the mobility of the center of mass of granular flows and (3) the wider the channel, the larger the mobility of the center of mass of granular flows. The grain size effect is due to the fact that finer grain size flows dissipate intrinsically less energy. This volume effect is the opposite of that experienced by the flow fronts. The original contribution of this paper consists of providing a comparison of the mobility of granular flows in six channels with a different cross section each. This results in a new scaling parameter χ that has the product of grain size and the cubic root of flow volume as the numerator and the product of channel width and flow length as the denominator. The linear correlation between the reciprocal of mobility and parameter χ is statistically highly significant. Parameter χ confirms that the mobility of the center of mass of granular flows is an increasing function of the ratio of the number of fragments per unit of flow mass to the total number of fragments in the flow. These are two characteristic numbers of particles whose effect on mobility is scale invariant.

Grain size dependence of the thermal conductivity of polycrystalline chemical vapor deposited β-SiC at low temperatures

Thermal conductivity data of polycrystalline chemical vapor deposited cubic silicon carbide are calculated from thermal diffusivity and heat capacity data in the temperature region of 80–300 K. Below 200 K, a linear dependence of the thermal conductivity with the product of grain size of the silicon carbide and cubic temperature is observed. This is explained in terms of phonon scattering by the grain boundaries.

Measurements and interpretation of the electrical resistivity and Hall coefficient in polycrystalline gold films: Part I

By measuring the resistivity of gold films as a function of temperature, the phonon contribution can be separated from the intrinsic one. The temperature dependence of the phonon terms can be fitted to a Sondheimer plot with the bulk electron mean free path and the value of the scattering parameter p varying with temperature. The phonon term at room temperature is not very different from the bulk. The intrinsic term in the resistivity is important, and in very thin films even more important than the phonon contribution. Electron microscopy including automatic image processing has shown that the product of grain size and intrinsic resistivity is constant. This agrees with the mosaic theory fairly well.