Now showing items 10530-10549 of 20709

    • K-Ar dating of rocks on Mars: Requirements from Martian meteorite analyses and isochron modeling

      Bogard, D. D. (The Meteoritical Society, 2009-01-01)
      Radiometric age dating of Martian rocks and surfaces at known locations for which crater densities can be determined is highly desirable in order to fully understand Martian history. Performing K-Ar age dating of igneous rocks on Mars by robots, however, presents technical challenges. Some of these challenges can be defined by examining Ar-Ar data acquired on Martian meteorites, and others can be evaluated through numerical modeling of simulated K-Ar isochrons like those that would be acquired robotically on Martian rocks. Excess 40Ar is present in all shergottites. Thus for Martian rocks, the slopes of K-Ar isochrons must be determined to reasonable precision in order to calculate reliable ages. Model simulations of possible isochrons give an indication of some requirements in order to define a precise rock age: Issues addressed here are: how many K-Ar analyses should be made of rocks thought to have the same age; what range of K concentrations should these analyzed samples have; and what analytical uncertainty in K-Ar measurements is desirable. Meteorite data also are used to determine the D/a^2 diffusion parameters for Ar in plagioclase and pyroxene separates of several shergottites and nakhlites. These data indicate the required temperatures and times for heating similar Martian rocks in order to extract Ar. Quantitatively extracting radiogenic 40Ar could be difficult, and degassing cosmogenic Ar from mafic phases even more so. Considering all these factors, robotic K-Ar dating of Martian rocks may be achievable, but will be challenging.
    • The Kadota Fig

      Kinnison, A. F. (College of Agriculture, University of Arizona (Tucson, AZ), 1928-03)
    • KAERI Radiocarbon Measurements III

      Pak, Chan Kirl; Yang, Kyung Rin (American Journal of Science, 1974-01-01)
    • Kangaroo Rats

      Sjoberg, Diana E.; Young, James A.; McAdoo, Kent; Evans, Raymond A. (Society for Range Management, 1984-02-01)
    • Kangaroos in Australian Rangelands

      Grice, A. C.; Beck, R. F. (Society for Range Management, 1994-10-01)
    • Kappa Omicron Pi Sends Delegate

      Woods, Ruth (College of Agriculture, University of Arizona (Tucson, AZ), 1928-03)
    • Karoo Desert National Botanical Garden

      Oliver, Ian; Karoo Botanical Garden (University of Arizona (Tucson, AZ), 2003-06)
    • Karoobush defoliation in the arid Karoo

      Du Toit, P. C. V. (Society for Range Management, 1996-03-01)
      The relation was studied between the applied stocking rates and the degree to which sheep grazed stems of various karoobush species. A rule of thumb exists amongst farmers and research workers in the Karoo, that sheep graze stems of karoobushes with a diameter of 2 mm or less. This hypothesis was examined over a period of 3 years. The meetly grazed off stems of Pentzia spinescens Less. (doringkaroo) and Rosenia humilis (Less.) Bremer (blou perdekaroo), the most abundant forage species, were measured by sliding Vernier callipers. Estimates of grazeable dry matter, as used in the estimate of the current grazing capacity, is based on the separation of clipped dry matter into grazeable and non-grazeable material. This separation is based on the 2 mm criterion. The hypothesis that sheep voluntarily graze stems with a diameter of up to 2 mm was rejected. The stems of less palatable species are seldom grazed at 2 mm diameter, while grazed stems of paintable species are often thicker than 5 mm. It was established that sheep graze stems of the less palatable karoo bushes to a mean diameter of 1.4 to 1.6 mm. This impacts directly on the method in which dry matter production is estimated for the purposes of determining grazing capacity. The long term grazing capacity norm for this area is 30 ha large stock unit-1. Based on gain ha-1 data obtained from stocking rate trials, the grazing capacity is 33.4 ha large stock unit-1. The stocking rate: grazed stem relation yields an optimum grazing capacity figure of 32.5 ha large stock unit-1. This indicates that monitoring the grazed stems of appropriate species can be used to set grazing capacity limits or adjust stocking rates.
    • Kazakhstan's Jury Experiment and beyond: Lessons from Emergent Systems of Lay Participation [Article]

      Fukurai, Hiroshi (The University of Arizona James E. Rogers College of Law (Tucson, AZ), 2019)
    • Ke yox hitamtaaycaqa ciiqinpa (that which is reported in talk): reported speech in Nez Perce

      Cash Cash, Phillip; University of Arizona (University of Arizona Linguistics Circle (Tucson, Arizona), 2004)
      This paper is a study of reported speech in Nez Perce (Sahaptian), an endangered language presently spoken in the southern Columbia Plateau region of western North America. This paper will focus on the use of reported speech in Nez Perce narrative to determine 1) the range and types of reported speech registers, and 2) discern how such reported speech registers might be patterned so as to indicate their cultural functions.
    • Keep 'Em Healthy

      Pistor, W. J. (College of Agriculture, University of Arizona (Tucson, AZ), 1952)
    • Keep an Eye on Your Keys

      Mattox, Matt (Society for Range Management, 2006-02-01)
    • Keeping Literature Alive

      Zinnel, Vera; Hofstra University (Worlds of Words: Center for Global Literacies and Literatures (University of Arizona), 2013-11)
    • Keeping Native American Communities Connected to the Land: Women as Change Agents

      Doan-Crider, Diana; Hipp, Janie Simms; Fight, Lisa Lone; Small, Valerie; Ashley, Virginia Yazzie (Society for Range Management, 2013-12-02)
      On the Ground • Native women are the fastest growing demographic among Native farmers and ranchers and have the ability, creativity, and cultural wealth to transform and restore the relationship to the land. • However, these women must be empowered in a western agricultural world that is male dominated. • Tribal self-sustainability will require changes in policies for land tenure and inclusion of women. • Native women will need to keep abreast of local and national land issues that affect our resources and that increase their knowledge and skills. • Education will give Native women and our youth the freedom to choose what is best for the future.
    • Keeping Small Horse Pastures Productive

      Stiger, Everett M. (Society for Range Management, 1994-06-01)
    • Keeping the Estate Tax

      McCann, Sean (Society for Range Management, 1999-01-01)
    • Keeping the Range in Range Cattle Production

      Banister, Ray (Society for Range Management, 1996-02-01)
    • Keeping the Sea Out: Early Medieval Structures at Ca’ Foscari University, Venice, Italy

      Meadows, John; Martinelli, Nicoletta; Pignatelli, Olivia; Cester, Rossella; Fozzati, Luigi; Kromer, Bernd (Department of Geosciences, The University of Arizona, 2012-10-15)
      In 2004, the courtyard of Ca’ Foscari University, Venice, was excavated in advance of building work, revealing an unbroken sequence of archaeological deposits. The earliest layers consisted of redeposited natural sediment, packed into wattle structures, a system of land reclamation first described by Cassiodorus in AD 537–8, and now known from several other sites in the city. The ground level was built up and extended several times with successive wattle structures, before the eventual construction of a stone waterfront. We have used Bayesian modeling of dendrochronological, radiocarbon, and stratigraphic dating evidence to obtain a precise chronology for the earliest phases of occupation, and to compare it to the chronology of land reclamation at similar sites elsewhere in Venice.
    • Keeping Them Down on the Farm

      College of Agriculture, University of Arizona (Tucson, AZ), 1989
    • Keeping Track of Weed Research By Computer

      Bowes, Gary; Hunter, Jim; Honey, G. K. (Society for Range Management, 1979-08-01)