25,302 research outputs found
Remembering Lee Ann in South Africa: Meta-data and reflexive research practice
Lee Ann Fujii and I became fast friends, colleagues, and disciplinary comrades soon after we met at the 2004 Institute for Qualitative and Multi-Method Research (IQMR). IQMR presentations and workshops sparked fourteen years of conversation about the discipline, our positionality with respect to the discipline and research participants, methodologies, the “field,” and much more. Lee Ann made me laugh and encouraged me to think harder as we talked over coffee and chocolate at home in Oakland, New York, Washington, DC, Indianapolis, and Toronto; met up at APSA annual meetings; and practiced yoga together
Finite difference time domain grid generation from AMC helicopter models
A simple technique is presented which forms a cubic grid model of a helicopter from an Aircraft Modeling Code (AMC) input file. The AMC input file defines the helicopter fuselage as a series of polygonal cross sections. The cubic grid model is used as an input to a Finite Difference Time Domain (FDTD) code to obtain predictions of antenna performance on a generic helicopter model. The predictions compare reasonably well with measured data
Soil Nitrogen and Carbon in Urban and Rural Forests
Previous work by Dr. Nancy Broshot has revealed high tree mortality and low recruitment (new seedlings) in an urban forest (Forest Park in Portland, Oregon). A series of lichen surveys in 2013 showed the lichen community has shifted to one dominated by lichens tolerant of and thriving on high nitrogen levels. To ascertain if nitrogenous air pollution could be a cause of low recruitment, we measured the level of nitrogen and carbon in the soil at 32 sites in Forest Park (24 permanent sites and 8 conifer recruitment sites). We also added 3 control sites in the Mount Hood National Forest above Estacada along an apparent air pollution gradient. The plant community was measured at three transects at each control site and lichen surveys were conducted. Four soil samples were collected at each site, dried at 35oC until weight remained constant and sieved to reduce to fine soil particle size. The samples will be assessed using an elemental analyzer to determine total nitrogen and total carbon
Size effects and dislocation patterning in two-dimensional bending
We perform atomistic Monte Carlo simulations of bending a Lennard-Jones
single crystal in two dimensions. Dislocations nucleate only at the free
surface as there are no sources in the interior of the sample. When
dislocations reach sufficient density, they spontaneously coalesce to nucleate
grain boundaries, and the resulting microstructure depends strongly on the
initial crystal orientation of the sample. In initial yield, we find a reverse
size effect, in which larger samples show a higher scaled bending moment than
smaller samples for a given strain and strain rate. This effect is associated
with source-limited plasticity and high strain rate relative to dislocation
mobility, and the size effect in initial yield disappears when we scale the
data to account for strain rate effects. Once dislocations coalesce to form
grain boundaries, the size effect reverses and we find that smaller crystals
support a higher scaled bending moment than larger crystals. This finding is in
qualitative agreement with experimental results. Finally, we observe an
instability at the compressed crystal surface that suggests a novel mechanism
for the formation of a hillock structure. The hillock is formed when a high
angle grain boundary, after absorbing additional dislocations, becomes unstable
and folds to form a new crystal grain that protrudes from the free surface.Comment: 15 pages, 8 figure
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