Whole object surface area and volume of micro-scale 3-D models with “hidden surface”

Micro-scale 3D models, important components of many studies in science and engineering, are often used to determine morphological characteristics such as shape, surface area and volume. The application of techniques such as stereoscopic scanning electron microscopy on whole objects often results in \u27partial-view\u27 models with a portion of object not within the field of view thus not captured in the 3D model. The nature and extent of the surface not captured is dependent on the complex interaction of imaging system attributes (e.g. working distance, viewing angle) with object size, shape and morphology. As a result, any simplistic assumptions in estimating whole object surface area or volume can lead to significant errors. In this study, we report on a novel technique to estimate the physical fraction of an object captured in a partial-view 3D model of an otherwise whole object. This allows a more accurate estimate of surface area and volume. Using 3D models, we demonstrate the robustness of this method and the accuracy of surface area and volume estimates relative to true values

Sizing up the bubbles that produce very fine ash during explosive volcanic eruptions

Explosive volcanic eruptions emit large proportions of very fine ash (\u3c30 μm) into the atmosphere, posing hazards to aviation, infrastructure, and human health. Here we present an analysis of bubble size distributions at the point of fragmentation during the 18 May 1980 eruption of MSH through the examination of simple ash particles in distally deposited fall samples. The external surfaces of individual fine ash grains preserve the morphology of the bubbles that burst to form the ash, so bubble sizes can be measured using stereo-scanning electron microscopy. Simple ash particles are those that allow the measurement of a single vesicle imprint per individual grain. These simple ash particles are the finest component of the tephra, and can thus travel great distances from the source volcano. Analyses of samples provided bubble volume distributions with a dominant peak between 560 and 5600μm3, corresponding to equivalent vesicle diameter modes of 10–22 μm, and these values were consistent for all examined sample locations. Determination of syn-eruptive bubble sizes thus makes it possible to glean information regarding conduit dynamics at the point of magma fragmentation from observed ash deposits, to parameterize numerical eruption models in ways not previously possible, and to quantify the size of bubbles that burst to create the ash component most hazardous to the aviation industry and human health

Explaining discontinuous garnet zoning using reaction history p-t models: an example from the Salmon River suture zone, west-central Idaho

Discontinuously zoned or two-stage garnet has been observed in numerous locations and geologic settings worldwide. These garnets are characterized by sharp breaks in inclusion density and compositional zoning, and often, these sharp breaks are interpreted as a hiatus in growth, change in growth rate, change in bulk rock composition, chemical diffusion, or absorption and new growth of garnet. During accretion of terranes and microplates, thermal pulses and thrust fault movements occur, which drive metamorphism and therefore the growth of garnet. Multiple garnet growth events could produce a discontinuously zoned garnet and each growth stage could be interpreted to represent a separate metamorphic event. Two-stage garnet is common in the Salmon River suture zone (SRSZ) and multiple tectonic models have been proposed based on the two-stage garnet. Getty et al. (1993) and Selverstone et al. (1992) proposed multiple accretion and metamorphic events based on the estimates for pressure, temperature, and age of these garnets. Recently, McKay (2011) proposed that heating after several major fault displacements caused the growth of two-stage garnet. This study uses compositions of garnet cores and rims on isochemical phase diagrams to construct new garnet growth P-T paths. Core and rim P-T estimates combined with observed mineral assemblages indicate an initial garnet growth reaction, followed by a reaction consuming and then growing garnet, e.g., chlorite + garnet = amphibole + H2O and amphibole = garnet + Al2SiO5 (kyanite) + H2O. Isochemical P-T modeling of garnet modal percentages, mineral compositions, and petrologic observations supports the occurrence of these reactions in the SRSZ garnet. The proposed reaction history would produce two-stage garnet along a single prograde path, which does not require multiple thermal and tectonic events. This interpretation supports the single terrane accretion hypothesis proposed by McKay (2011). (Published By University of Alabama Libraries