Now showing items 7241-7260 of 20719

    • Exposition on the Selection of Appropriate Experimental Design and Statistical Analysis for Pasture Improvement Research

      Stroup, W. W.; Waller, S. S.; Gates, R. N. (Society for Range Management, 1986-05-01)
      Selection of appropriate treatment and experiment designs are essential elements in research. However, the expense and variability associated with pasture renovation studies creates unique problems in the application of standard statistical techniques. Pasture-size renovation studies are restricted by expense, requiring the use of grazing exclosures (subsamples). Treatment design must include an adequate control for treatment comparison. Controls for pasture renovation practices cannot be limited to untreated areas within a grazing exclosure. The true measure response is found in the difference between treated areas and a typical grazed pasture situation. Criteria for exclosure selection (homogeneity) and heterogeneity of the grazed pasture may result in unequal variances or nonnormal error distributions, thus restricting the use of an analysis of variance. The experiment design must recognize the requirements for making reliable inferences. Pasture-to-pasture variability generally demands that pastures should be replicated in renovation studies to allow general inferences. Within pasture variability would support the need for multiple exclosures within each pasture. Costs associated with this kind of research limit the utility of idealized experimental designs. Several alternative experimental designs are discussed. Limitations in interpretation and risks of drawing erroneous or weak conclusions are reviewed.
    • Exposure history and terrestrial ages of ordinary chondrites from the Dar al Gani region, Libya

      Welten, K. C.; Nishiizumi, K.; Finkel, R. C.; Hillegonds, D. J.; Jull, A. J. T.; Franke, L.; Schultz, L. (The Meteoritical Society, 2004-01-01)
      We measured the concentrations of noble gases in 32 ordinary chondrites from the Dar al Gani (DaG) region, Libya, as well as concentrations of the cosmogenic radionuclides 14C, 10Be, 26Al, 36Cl, and 41Ca in 18 of these samples. Although the trapped noble gases in five DaG samples show ratios typical of solar or planetary gases, in all other DaG samples, they are dominated by atmospheric contamination, which increases with the degree of weathering. Cosmic ray exposure (CRE) ages of DaG chondrites range from ~1 Myr to 53 Myr. The CRE age distribution of 10 DaG L chondrites shows a cluster around 40 Myr due to four members of a large L6 chondrite shower. The CRE age distribution of 19 DaG H chondrites shows only three ages coinciding with the main H chondrite peak at ~7 Myr, while seven ages are <5 Myr. Two of these H chondrites with short CRE ages (DaG 904 and 908) show evidence of a complex exposure history. Five of the H chondrites show evidence of high shielding conditions, including low 22Ne/21Ne ratios and large contributions of neutron-capture 36Cl and 41Ca. These samples represent fragments of two or more large pre-atmospheric objects, which supports the hypothesis that the high H/L chondrite ratio at DaG is due to one or more large unrecognized showers. The 14C concentrations correspond to terrestrial ages <35 kyr, similar to terrestrial ages of chondrites from other regions in the Sahara but younger than two DaG achondrites. Despite the loss of cosmogenic 36Cl and 41Ca during oxidation of metal and troilite, concentrations of 36Cl and 41Ca in the silicates are also consistent with 14C ages <35 kyr. The only exception is DaG 343 (H4), which has a 41Ca terrestrial age of 150 +/- 40 kyr. This old age shows that not only iron meteorites and achondrites but also chondrites can survive the hot desert environment for more than 50 kyr. A possible explanation is that older meteorites were covered by soils during wetter periods and were recently exhumed by removal of these soils due to deflation during more arid periods, such as the current one, which started ~3000 years ago.Finally, based on the 26Al/21Ne and 10Be/21Ne systematics in 16 DaG meteorites, we derived more reliable estimates of the 10Be/21Ne production rate ratio, which seems more sensitive to shielding than was predicted by the semi-empirical model of Graf et al. (1990) but less sensitive than was predicted by the purely physical model of Leya et al. (2000).
    • Exposure May Influence Grassland Establishment

      Dillion, Claude C. (Society for Range Management, 1967-03-01)
      This example of the effect of exposure to grassland establishment can be useful to range management. South exposure sites in this climate will only recover to annual vegetation if perennial plants have been destroyed-that is, within a reasonable period of years. Reseeding would be an important consideration. Deferred grazing may not be beneficial on south exposure sites, but very desirable on north exposures where an excellent perennial grass stand could develop.
    • Expressing the Competitive Relationship between Wyoming Big Sagebrush and Crested Wheatgrass

      Rittenhouse, L. R.; Sneva, F. A. (Society for Range Management, 1976-07-01)
      Crested wheatgrass production was negatively correlated with Wyoming big sagebrush crown cover. Each 1% increase in sagebrush crown cover was associated with a decline in crested wheatgrass production equivalent to 3.3 to 5.2% of its potential within the range of cover measured. Expression of this relationship in the above manner may enable sounder economic analysis than conventional methods now used.
    • Extended 14C Data Base and Revised CALIB 3.0 14C Age Calibration Program

      Stuiver, Minze; Reimer, Paula J. (Department of Geosciences, The University of Arizona, 1993-01-01)
    • Extended grazing systems for improving economic returns from Nebraska sandhills cow/calf operations

      Adams, D. C.; Clark, R. T.; Coady, S. A.; Lamb, J. B.; Nielsen, M. K. (Society for Range Management, 1994-07-01)
      Three winter treatments were cross classified with 2 spring treatments to create 6 feeding and grazing systems utilizing Nebraska sandhills range and subirrigated meadow forage. Systems were evaluated with multiparous crossbred beef cows over 4 years (240 head beginning year 1). Systems were: 1) owing range during winter; 2) grazing subirrigated meadow during winter; and 3) fur feed of meadow bay during winter; in combination with either: a) full feed of subirrigated meadow hay during May, or b) grazing subirrigated meadow during May. From June through November all cows grazed range. The feeding and grazing systems were compared with selected linear contrasts and evaluated with respect to variable input prices. Some differences in cow body weight and body condition occurred but differences were considered small. Throughout the study, cows on all systems generally maintained a body condition score of about 5 (1 to 9 scale) year long. Inputs of hay were reduced by grazing range or subirrigated meadow during winter and during May without affecting pregnancy rate. Weaning weight of calves was increased 5.0 kg by grazing meadow during May compared to feeding hay during May. When opportunity costs were included in the analysis, the most profitable system involved grazing subirrigated meadow during winter and during May. Grazing subirrigated meadow during May enhanced the profitability of all wintering systems.
    • Extended Radiocarbon Calibration in the Anglo-Saxon Period, AD 395-485 and AD 735-805

      McCormac, F. G.; Bayliss, A.; Brown, D. M.; Reimer, P. J.; Thompson, M. M. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Radiocarbon dating has been used infrequently as a chronological tool for research in Anglo-Saxon archaeology. Primarily, this is because the uncertainty of calibrated dates provides little advantage over traditional archaeological dating in this period. Recent advances in Bayesian methodology in conjunction with high-precision 14C dating have, however, created the possibility of both testing and refining the established Anglo-Saxon chronologies based on typology of artifacts. The calibration process within such a confined age range, however, relies heavily on the structural accuracy of the calibration curve. We have previously reported decadal measurements on a section of the Irish oak chronology for the period AD 495-725 (McCormac et al. 2004). In this paper, we present decadal measurements for the periods AD 395-485 and AD 735-805, which extends the original calibration set.
    • Extending Thinking: Literature Response through Art

      Edwards, Amy D.; Van Horne Elementary School (Worlds of Words: Center for Global Literacies and Literatures (University of Arizona), 2007-10)
    • Extending Wetlands Protection under the Ramsar Treaty's Wise Use Obligation [Note]

      Kruchek, Beth L. (The University of Arizona James E. Rogers College of Law (Tucson, AZ), 2003)
    • Extension Advice Saves On Farm Income Taxes

      Campbell Jr., George W.; Extension Economy (College of Agriculture, University of Arizona (Tucson, AZ), 1964)
    • Extension Expands Educational Resources

      Myers, Harold E.; College of Agriculture (College of Agriculture, University of Arizona (Tucson, AZ), 1972)
    • Extension of the 14C Calibration Curve to ca. 40,000 cal BC by Synchronizing Greenland 18O/16O Ice Core Records and North Atlantic Foraminifera Profiles: A Comparison with U/Th Coral Data

      Jöris, Olaf; Weninger, Bernhard (Department of Geosciences, The University of Arizona, 1998-01-01)
      For a better understanding of pre-Holocene cultural history, archaeologists are in need of an absolute time scale that can be confirmed and duplicated by different dating methods. Proxy data available from archaeological sites do not, in themselves, allow much reflection on absolute age. Even when founded on supporting radiocarbon data, Paleolithic chronologies that are beyond the actual limits of 14C calibration still remain relative ones, and thus are often quite tentative. Lacking the possibility of calibration for the Paleolithic, archaeologists often attempt to correlate their data with different time scales from different archives that are thought to be absolute or calendric. The main result of this paper is that the GISP2 and U/Th chronologies duplicate each other over their entire range of data overlap, while other time scales (i.e., GRIP, most varve sites) differ significantly. The context-derived 14C calibration curve provides a large potential to correlate the various climate archives as recorded in ice cores and deep ocean drillings with terrestrial sequences.
    • An Extension of the Durango Chronology

      Schulman, Edmund (Tree-Ring Society, 1949-10)
    • Extension of the Holocene Dendrochronology by the Preboreal Pine Series, 8800 to 10,100 BP

      Becker, Bernd; Kromer, Bernd (American Journal of Science, 1986-01-01)
      Holocene tree-ring chronologies have been established for south-central Europe covering the past 11,000 years. The Hohenheim absolute oak chronology extends to 4089 BC. The 14C-calibrated mid-Holocene floating oak master covers a 3181-year period from ca 4045 to 7225 BC. The earliest well-replicated floating oak master (estimated calendar age 7215 to 7825 BC) extends the European oak dendrochronology back to Boreal times. Further extension of the Holocene dendrochronology has been achieved by subfossil oak and pine trees from the Rhine, Main, and Danube Rivers. A 774-year floating series of Preboreal pine has been established. 14C ages range (from younger to older end) from 9200 to 9800 BP. Within this series a major atmospheric 14C variation is indicated, resulting in nearly constant 14C ages (9600 BP) over a period of 370 tree-rings. The European oak and pine tree-ring chronologies cover without major gaps the entire Holocene epoch. Based on the length of the dendro-records, an approximate solar year age of 11,280 years is calculate for the Holocene/Pleistocene boundary. The Preboreal pine forests along the rivers were replaced by mixed oak forests between 9200 and 8800 BP. By linking the earliest oak masters and the Preboreal pine series, the European dendrochronology can be extended up to the end of Late Glacial times.
    • Extension of the San Juan Chronology to B.C. Times

      Schulman, Edmund (Tree-Ring Society, 1952-04)
    • Extension of the Southern Hemisphere Atmospheric Radiocarbon Curve, 2120-850 Years BP: Results from Tasmanian Huon Pine

      Zimmerman, Susan; Guilderson, Thomas; Buckley, Brendan; Cook, Edward (Department of Geosciences, The University of Arizona, 2010-01-01)
      Decadal samples of dendrochronologically dated pine (Lagorostrobos franklinii) from the Stanley River basin, Tasmania, have been radiocarbon dated between 2120-850 yr BP. This data set overlaps and extends the current Southern Hemisphere record, which covers the period 110-995 yr BP. There is good agreement between the 2 records between 995-850 yr BP, between sample replicates and with consensus values for standards. As in the younger data set, we find evidence for a distinct but variable offset between the Southern Hemisphere data and IntCal04; although this is likely due to real temporal variability in the interhemispheric offset, further work is planned to rule out possible laboratory or sample preparation differences.
    • Extension Practices for Range Management at Abilene Christian College, Abilene, Texas

      Churchill, F. M. (Society for Range Management, 1951-09-01)
    • Extension Program at Ceara Basic, Active and Helpful

      Ray, Howard; Agricultural Extension Service (College of Agriculture, University of Arizona (Tucson, AZ), 1964)
    • Extension Range Work in Texas

      Walker, A. H. (Society for Range Management, 1950-07-01)
    • Extension Service Home Demonstration

      Stewart, Jean M.; Agricultural Extension Service (College of Agriculture, University of Arizona (Tucson, AZ), 1957)