7 research outputs found
Some Trends in College Physics and Their Reflections on High School Physics
We are much struck with the desirable results that follow from introducing brief discussions of modern physics topics during the course of ordinary, relatively routine first courses in physics for college freshmen and sophomores. We propose in this paper that teachers of secondary physics courses might well also consider the incorporation of such discussions into their courses
Remote Sensing of Ploidy Level in Quaking Aspen (Populus Tremuloides Michx.)
Ploidy level in plants may influence ecological functioning, demography and response to climate change. However, measuring ploidy level typically requires intensive cell or molecular methods. We map ploidy level variation in quaking aspen, a dominant North American tree species that can be diploid or triploid and that grows in spatially extensive clones. We identify the predictors and spatial scale of ploidy level variation using a combination of genetic and ground‐based and airborne remote sensing methods. We show that ground‐based leaf spectra and airborne canopy spectra can both classify aspen by ploidy level with a precision‐recall harmonic mean of 0.75–0.95 and Cohen\u27s kappa of c. 0.6–0.9. Ground‐based bark spectra cannot classify ploidy level better than chance. We also found that diploids are more common on higher elevation and steeper sites in a network of forest plots in Colorado, and that ploidy level distribution varies at subkilometer spatial scales. Synthesis. Our proof‐of‐concept study shows that remote sensing of ploidy level could become feasible in this tree species. Mapping ploidy level across landscapes could provide insights into the genetic basis of species\u27 responses to climate change
Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece
Zircon U-Pb dating is a powerful and widely used geochronologic
technique to constrain the timing and rates of magmatic and high and
lower-grade metamorphic processes, as well as sediment provenance.
Zircon trace element (TE) compositions also record magmatic and
metamorphic processes during zircon growth. In this study, zircon laser
ablation split-stream (LA-SS)-ICP-MS U-Pb and TE depth-profiling and
novel two-dimensional zircon mapping techniques are used in combination
with oxygen isotope analyses (secondary ion mass spectrometry, SIMS) to
reconstruct the timing and metamorphic conditions recorded by
recrystallization and growth of zircon rims, which provide valuable
insight into the petro-tectonic evolution of
high-pressure/low-temperature (HP/LT) metamorphic rocks formed in
subduction zones. These techniques are applied to zircon grains from
HP/LT metamorphic rocks of the Cycladic Blueschist Unit (CBU) and
Cycladic Basement (CB) on Sikinos and Ios islands, Greece, which
experienced metamorphism and deformation associated with subduction and
subsequent back-arc exhumation. Zircon records multiple episodes of
non-magmatic zircon rim growth at similar to 50 Ma and similar to 26 Ma.
Eocene metamorphic rims are associated with HP/LT metamorphism and are
observed in both units, suggesting likely juxtaposition prior to or
during subduction and associated HP metamorphism. The similarity between
TE concentrations and delta O-18 values of the Eocene rims and their
corresponding cores is an indicator for recrystallization and
precipitation as a mechanism of zircon growth. In contrast, Oligocene
zircon rims appear to be restricted to a < 0.5 km thick zone along the
CB-CBU contact, characterized by garnet break-down, and show HREE
enrichment and higher delta O-18 values in the rims compared to the
cores, consistent with a model suggesting metasomatic infiltration of
fluids derived from dehydrating sedimentary rocks during progressive
subduction and underplating prior to back-arc extension. This
metamorphism appears to be static in nature and does not support major
late Cenozoic reactivation of the contact as an extensional shear zone
during back-arc extension