41 research outputs found
The demography of range boundaries versus range cores in eastern US tree species
Regional speciesâclimate correlations are well documented, but little is known about the ecological processes responsible for generating these patterns. Using the data from over 690â000 individual trees I estimated five demographic ratesâcanopy growth, understorey growth, canopy lifespan, understorey lifespan and per capita reproductionâfor 19 common eastern US tree species, within the core and the northern and southern boundaries, of the species range. Most species showed statistically significant boundary versus core differences in most rates at both boundary types. Differences in canopy and understorey growth were relatively small in magnitude but consistent among species, being lower at the northern (average â17%) and higher at the southern (average +12%) boundaries. Differences in lifespan were larger in magnitude but highly variable among species, except for a marked trend for reduced canopy lifespan at the northern boundary (average â49%). Differences in per capita reproduction were large and statistically significant for some species, but highly variable among species. The rate estimates were combined to calculate two performance indices: R0 (a measure of lifetime fitness in the absence of competition) was consistently lower at the northern boundary (average â86%) whereas Z* (a measure of competitive ability in closed forest) showed no sign of a consistent boundaryâcore difference at either boundary
Enhanced generation of VUV radiation by four-wave mixing in mercury using pulsed laser vaporization
The efficiency of a coherent VUV source at 125 nm, based on 2-photon resonant
four-wave mixing in mercury vapor, has been enhanced by up to 2 orders of
magnitude. This enhancement was obtained by locally heating a liquid Hg surface
with a pulsed excimer laser, resulting in a high density vapor plume in which
the nonlinear interaction occurred. Energies up to 5 μJ (1 kW peak power)
have been achieved while keeping the overall Hg cell at room temperature,
avoiding the use of a complex heat pipe. We have observed a strong saturation
of the VUV yield when peak power densities of the fundamental beams exceed the
GW/cm2 range, as well as a large intensity-dependant broadening (up to ~30
cm-1) of the two-photon resonance. The source has potential applications for
high resolution interference lithography and photochemistry
Mountain ridgeline
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Rocky Mountains, Lemhi Valley, about 10 miles south of Salmon City
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Salmon River a few miles north of Challis (Looking north)
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Dome Peak, Salmon River Mountains from Little Lost River Valley
This is image is part of records by Fish and Wild Life Services