1,880 research outputs found
Stellar Population Effects on the Inferred Photon Density at Reionization
The relationship between stellar populations and the ionizing flux with which
they irradiate their surroundings has profound implications for the evolution
of the intergalactic medium. We quantify the ionizing flux arising from
synthetic stellar populations which incorporate the evolution of interacting
binary stars. We determine that these show ionizing flux boosted by 60 per cent
at 0.05 < Z < 0.3 Z_sun and a more modest 10-20 per cent at near-Solar
metallicities relative to star-forming populations in which stars evolve in
isolation. The relation of ionizing flux to observables such as 1500A continuum
and ultraviolet spectral slope is sensitive to attributes of the stellar
population including age, star formation history and initial mass function. For
a galaxy forming 1 M_sun yr^{-1}, observed at > 100 Myr after the onset of star
formation, we predict a production rate of photons capable of ionizing
hydrogen, N_ion = 1.4 x 10^{53} s^{-1} at Z = Z_sun and 3.5 x 10^{53} s^{-1} at
0.1 Z_sun, assuming a Salpeter-like initial mass function. We evaluate the
impact of these issues on the ionization of the intergalactic medium, finding
that the known galaxy populations can maintain the ionization state of the
Universe back to z ~ 9, assuming that their luminosity functions continue to
M_UV = -10, and that constraints on the intergalactic medium at z ~ 2 - 5 can
be satisfied with modest Lyman continuum photon escape fractions of 4 - 24 per
cent depending on assumed metallicity.Comment: 17 pages, accepted by MNRAS. BPASS models can be found at
http://bpass.auckland.ac.nz
Arkansas Soybean Performance Tests 2008
Soybean cultivar performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies developing cultivars and/or marketing seed within the state, and aid the Arkansas Cooperative Extension Service in formulating cultivar recommendations for soybean producer
Arkansas Soybean Performance Tests 2007
Soybean cultivar performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies developing cultivars and/or marketing seed within the State, and aid the Arkansas Cooperative Extension Service in formulating cultivar recommendations for soybean producers
Arkansas Corn and Grain Sorghum Performance Tests 2003
Corn and grain sorghum performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies marketing seed within the state, and aid the Arkansas Cooperative Extension Service in formulating recommendations for producers
Stratospheric measurement requirements and satellite-borne remote sensing capabilities
The capabilities of specific NASA remote sensing systems to provide appropriate measurements of stratospheric parameters for potential user needs were assessed. This was used to evaluate the capabilities of the remote sensing systems to perform global monitoring of the stratosphere. The following conclusions were reached: (1) The performance of current remote stratospheric sensors, in some cases, compares quite well with identified measurement requirements. Their ability to measure other species has not been demonstrated. (2) None of the current, in-situ methods have the capability to satisfy the requirements for global monitoring and the temporal constraints derived from the users needs portion of the study. (3) Existing, non-remote techniques will continue to play an important role in stratospheric investigations for both corroboration of remotely collected data and in the evolutionary development of future remote sensors
Arkansas Corn and Grain Sorghum Performance Tests 2009
Corn and grain sorghum performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating recommendations for producers
Arkansas Corn and Grain Sorghum Performance Tests 2007
Corn and grain sorghum performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies marketing seed within the state, and aid the Arkansas Cooperative Extension Service in formulating recommendations for producers
Arkansas Corn and Grain Sorghum Performance Tests 2008
Corn and grain sorghum performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture. The tests provide information to companies marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating recommendations for producers
Arkansas Soybean Performance Tests 2009
Soybean variety and strain performance tests are conducted each year in Arkansas by the University of Arkansas Division of Agriculture Arkansas Crop Variety Improvement Program. The tests provide information to companies developing varieties and/or marketing seed within the state, and aid the Arkansas Cooperative Extension Service in formulating variety recommendations for soybean producers
- …