Browsing by Subject "scanning electron microscopy"
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Item Calcification in human arterial disease and geological specimens: The nannobacterial (nanoparticle) link(2013) Folk, Robert L.; Kirkland, Brenda L.; Rodgers, Jeri C.; Rodgers, George P.The biogenicity of calcium - phosphate - precipitating nannobacteria (nanobacteria, self - replicating nanoparticles) has been supported by researchers: the tiny cells (30 - 70 nm in diameter) reproduce in cultures, show cell walls in TEM, and react positively for DNA and immunostain. The recently documented cells bear remarkable resemblances to those found earlier in geologic settings such as hot springs, weathered volcanic rocks, travertines, sandstones, soils, and even a Martian meteorite. In this paper we focus on the similarities of the nannobacterial morphologies found in the biologic and geologic settings, as documented by high resolution SEM. In both settings nannobacteria occur as isolated cells, as chains or sheets of phosphatized cells, finally to form hard blocky masses of hydroxyapatite.Item Effects of Spatial Energy Distribution on Defects and Fracture of LPBF 316L Stainless Steel(University of Texas at Austin, 2019) Jost, Elliott; Miers, John; Robinson, Aron; Moore, David; Saldana, ChristopherMeasures of energy input and spatial energy distribution during laser powder bed fusion additive manufacturing have significant implications for the build quality of parts, specifically relating to formation of internal defects during processing. In this study, scanning electron microscopy was leveraged to investigate the effects of these distributions on the mechanical performance of parts manufactured using laser powder bed fusion as seen through the fracture surfaces resulting from uniaxial tensile testing. Variation in spatial energy density is shown to manifest in differences in defect morphology and mechanical properties. Computed tomography and scanning electron microscopy inspections revealed significant evidence of porosity acting as failure mechanisms in printed parts. These results establish an improved understanding of the effects of spatial energy distributions in laser powder bed fusion on mechanical performance.