Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V

Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process

Survey team on : conceptualisations of the role of competencies, knowing and knowledge in mathematics education research

This paper presents the outcomes of the work of the ICME 13 Survey Team on 'Conceptualisation and the role of competencies, knowing and knowledge in mathematics education research'. It surveys a variety of historical and contemporary views and conceptualisations of what it means to master mathematics, focusing on notions such as mathematical competence and competencies, mathematical proficiency, and mathematical practices, amongst others. The paper provides theoretical analyses of these notions-under the generic heading of mathematical competencies-and gives an overview of selected research on and by means of them. Furthermore, an account of the introduction and implementation of competency notions in the curricula in various countries and regions is given, and pertinent issues are reviewed. The paper is concluded with a set of reflections on current trends and challenges concerning mathematical competencie

State Water Resources Control Board

Chapter 9 presents only the references that are cited in this document (the Draft SEIS/REIR). Chapter 9 is being revised in response to public comments received on the Draft EIS/EIR. The complete revised chapter will be presented in th

Variation of summer phytoplankton community composition and its relationship to nitrate and regenerated nitrogen assimilation across the North Atlantic

The North Atlantic Ocean is considered a nitrogen (N) limited system once vernal stabilisation of the water column alleviates light limitation and allows phytoplankton growth to deplete surface nutrients to virtually undetectable levels. Ammonium and other regenerated N forms are then the main surface N source for phytoplankton production. The effort to determine which phytoplankton groups contribute to long-term biological export production would be greatly aided by information on which phytoplankton groups are responsible for the assimilation of nitrate, as opposed to those assimilating predominantly regenerated N. In this study, we used the natural abundance N isotopes to examine basin-scale patterns of nitrate and regenerated N assimilation and evaluated the relationships between these trends and phytoplankton community composition. Samples were collected during a summertime cruise transect (August–September 2013) from the subtropical (36°N 73°W) to the subarctic (54°N 20°W) North Atlantic and analysed for the N isotopic composition (δ15N vs. N2 in air) of particulate nitrogen (PN) and nitrate, size-fractionated chlorophyll a, and phytoplankton group biomass using flow cytometry. The depth of the 300 nmol l−1 nitrate isopleth shoaled from the subtropics (79 m), where phytoplankton stripped surface waters of nitrate, to the subarctic, where it intersected with the surface and the upward nutrient supply drove a summer phytoplankton bloom. The δ15N of PN above the nitracline increased from the subtropics (−0.3‰) to the subarctic (4.2‰), reflecting both a change in the δ15N of the subsurface nitrate source (from 2.4‰ to 5.1‰) and increased reliance by phytoplankton on nitrate relative to regenerated N. Throughout the transect, the phytoplankton community was mainly composed of pico- and nano-sized cells ( > 88% of chlorophyll a in the < 20 μm size fraction). In the part of the transect southwest of the Grand Banks, Prochlorococcus and Synechococcus together dominated the picophytoplankton biomass (58% and 18% on average) and comprised 35% and 9%, respectively, of combined pico- and nanophytoplankton biomass. Pico- and nanoeukaryotes showed the opposite pattern, becoming more important closer to the subarctic (up to 31% and 86% of combined pico- and nanophytoplankton biomass, respectively). The North Atlantic summertime patterns in N assimilation implied by the N isotopes were consistent with a higher degree of nitrate assimilation by larger eukaryotic cells and greater reliance on regenerated N by cyanobacterial picophytoplankton, congruent with the observed biomass distributions