6,648 research outputs found
4mu spectra of AGB stars I: Observations
We present times series of high resolution spectra of AGB variables at 4mu.
Line profiles from the major contributors to the spectra of oxygen rich stars
at 4mu, OH, HO, HCl and SiO, are examined. The velocity as well as shape
variations of these profiles with time are discussed. The line profiles
investigated frequently have emission and multiple absorption components. The
changes with time of the 4mu region lines do not always follow the cyclic
variability seen in NIR spectra and in the photometric light curve. We
interpret and discuss the results qualitatively considering comparing the
spectral variability with that of the well behaved 1.6mu region and of
dynamical model atmospheres. Miras and semiregular variables are compared. The
origins of non-periodic behavior are discussed, including the role of spatial
inhomogeneities in the stellar atmosphere.Comment: 14 pages, 12 figures, accepted for publication in A&
The NASA planetary biology internship experience
By providing students from around the world with the opportunity to work with established scientists in the fields of biogeochemistry, remote sensing, and origins of life, among others, the NASA Planetary Biology Internship (PBI) Program has successfully launched many scientific careers. Each year approximately ten interns participate in research related to planetary biology at NASA Centers, NASA-sponsored research in university laboratories, and private institutions. The PBI program also sponsors three students every year in both the Microbiology and Marine Ecology summer courses at the Marine Biological Laboratory. Other information about the PBI Program is presented including application procedure
Dynamics of vegetation and soils of oak/saw palmetto scrub after fire: Observations from permanent transects
Ten permanent 15 m transects previously established in two oak/saw palmetto scrub stands burned in December 1986, while two transects remained unburned. Vegetation in the greater than 0.5 m and the less than 0.5 m layers on these transects was sampled at 6, 12, 18, 24, and 36 months postburn and determined structural features of the vegetation (height, percent bare ground, total cover). The vegetation data were analyzed from each sampling by height layer using detrended correspondence analysis ordination. Vegetation data for the greater than 0.5 m layer for the entire time sequence were combined and analyzed using detrended correspondence analysis ordination. Soils were sampled at 6, 12, 18, and 24 months postburn and analyzed for pH, conductivity, organic matter, exchangeable cations (Ca, Mg, K, Na), NO3-N, NH4-N, Al, available metals (Cu, Fe, Mn, Zn), and PO4-P. Shrub species recovered at different rates postfire with saw palmetto reestablishing cover greater than 0.5 m within one year, but the scrub oaks had not returned to preburn cover greater than 0.5 m in 3 years after the fire. These differences in growth rates resulted in dominance shifts after the fire with saw palmetto increasing relative to the scrub oaks. Overall changes in species richness were minor, although changes occurred in species richness by height layers due to different growth rates. Soils of well drained and poorly drained sites differed markedly. Soil responses to the fire appeared minor. Soil pH increased at 6 and 12 months postfire; calcium increased at 6 months postburn. Nitrate-nitrogen increased at 12 months postburn. Low values of conductivity, PO4-P, Mg, K, Na, and Fe at 12 months postburn may be related to heavy rainfall the preceding month. Seasonal variability in some soil parameters appeared to occur
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