24,363 research outputs found
Where Have All the Young Trees Gone? A Big Picture Look at the Lack of Seedlings and Saplings in Urban Forests
We take a big picture look at the lack of seedlings, saplings and young trees in urban forests using our research in Forest Park in Portland, Oregon. Broshot, who measured vegetation at 25 sites in Forest Park, recorded significantly fewer live seedlings, saplings and young trees and significantly more dead seedlings, saplings and young trees in 2003 than in 1993. The percent mortality of western red cedar seedlings that were planted at 9 sites in Forest Park in 2005 ranged from less than 5% to over 70%. Investigations into the cause of seedling death has discounted predation by deer, elk or invertebrates, leaf disease, soil moisture, site aspect, and light as factors. The site with the highest mortality is located directly above the St John’s Bridge, suggesting air pollution. More recent work with lichens has provided evidence that nitrogen deposition related to air pollution may be the cause. We outline our past work and report preliminary results from our 2012 lichen survey analysis to support our hypothesis that pollution is a cause of the lack of young trees
RESEARCH NOTES AND APPLICATION REPORTS NITROGEN AND FLUORINE DATING OF MOUNDVILLE SKELETAL SAMPLES
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65569/1/j.1475-4754.1982.tb00645.x.pd
Gravity from the extension of spatial diffeomorphisms
The possibility of the extension of spatial diffeomorphisms to a larger
family of symmetries in a class of classical field theories is studied. The
generator of the additional local symmetry contains a quadratic kinetic term
and a potential term which can be a general (not necessarily local) functional
of the metric. From the perspective of the foundation of Einstein's gravity our
results are positive: The extended constraint algebra is either that of
Einstein's gravity, or ultralocal gravity. If our goal is a simple modification
of Einstein's gravity that for example makes it perturbatively renormalizable,
as has recently been suggested, then our results show that there is no such
theory within this class.Comment: 34 page
Inferring the three-dimensional distribution of dust in the Galaxy with a non-parametric method: Preparing for Gaia
We present a non-parametric model for inferring the three-dimensional (3D)
distribution of dust density in the Milky Way. Our approach uses the extinction
measured towards stars at different locations in the Galaxy at approximately
known distances. Each extinction measurement is proportional to the integrated
dust density along its line-of-sight. Making simple assumptions about the
spatial correlation of the dust density, we can infer the most probable 3D
distribution of dust across the entire observed region, including along sight
lines which were not observed. This is possible because our model employs a
Gaussian Process to connect all lines-of-sight. We demonstrate the capability
of our model to capture detailed dust density variations using mock data as
well as simulated data from the Gaia Universe Model Snapshot. We then apply our
method to a sample of giant stars observed by APOGEE and Kepler to construct a
3D dust map over a small region of the Galaxy. Due to our smoothness constraint
and its isotropy, we provide one of the first maps which does not show the
"fingers of god" effect.Comment: Minor changes applied. Final version accepted for publication in A&A.
15 pages, 17 figure
Torsion formulation of gravity
We make it precise what it means to have a connection with torsion as
solution of the Einstein equations. While locally the theory remains the same,
the new formulation allows for topologies that would have been excluded in the
standard formulation of gravity. In this formulation it is possible to couple
arbitrary torsion to gauge fields without breaking the gauge invariance.Comment: AMS-LaTeX, 25 pages. Appendices have been eliminated and the
necessary concepts have been inroduced in the text. We have added some
reference
Feasibility study of a 110 watt per kilogram lightweight solar array system
An investigation of the feasibility of a solar array panel subsystem which will produce 10,000 watts of electrical output at 1 A.U. with an overall beginning-of-life power-to-weight ratio of at least 110 watt/kg is reported. A description of the current baseline configuration which meets these requirements is presented. A parametric analysis of the single boom, two blanket planar solar array system was performed to arrive at the optimum system aspect ratio. A novel concept for the stiffening of a lightweight solar array by canting the solar cell blankets at a small angle to take advantage of the inherent in-plane stiffness to increase the symmetric out-of-plane frequency is introduced along with a preliminary analysis of the stiffening effect. A comparison of welded and soldered solar cell interconnections leads to the conclusion that welding is required on this ultralightweight solar array. The use of a boron/aluminum composite material in a BI-STEM type deployable boom is investigated as a possible advancement in the state-of-the-art
Soldered Bundle Background for the De Sitter Top
We prove that the mathematical framework for the de Sitter top system is the
de Sitter fiber bundle. In this context, the concept of soldering associated
with a fiber bundle plays a central role. We comment on the possibility that
our formalism may be of particular interest in different contexts including
MacDowell-Mansouri theory, two time physics and oriented matroid theory.Comment: 12 pages, Latex; some improvements introduced, reference added, typos
correcte
Air Pollution: The Trees Aren\u27t Lichen It
The Keck Summer Collaborative Research Program provides opportunities for Linfield College students and faculty to conduct research on issues related to the Pacific Northwest, and to bring the research findings back into the classroom within the subsequent academic year. Students partner with faculty to conduct research and present their work to other students, Linfield staff and faculty, and community members during a series of brown bag lunches. Wes Hanson, Leigh Hanson, Meghan Lockwood, and Morgan Yarber conducted research with Nancy Broshot and gave this presentation during the summer of 2013
The relationships between high latitude convection reversals and the energetic particle morphology observed by the Atmosphere Explorer
Simultaneous measurements of the auroral zone particle precipitation and the ion convection velocity by Atmosphere Explorer show a consistent difference between the location of the poleward boundary of the auroral particle precipitation and the ion convection reversal. The difference of about 1.5 degrees of invariant latitude is such that some part of the antisunward convection lies wholly within the auroral particle precipitation region. The nature of the convection reversals within the precipitation region suggests that in this region the convection electric field is generated on closed field lines that connect in the magnetosphere to the low latitude boundary layer
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