Now showing items 19667-19686 of 20709

    • Valence state partitioning of V between pyroxene-melt: Effects of pyroxene and melt composition, and direct determination of V valence states by XANES. Application to Martian basalt QUE 94201 composition

      Karner, J. M.; Papike, J. J.; Sutton, S. R.; Shearer, C. K.; Burger, P.; McKay, G.; Le, L. (The Meteoritical Society, 2008-01-01)
      Experiments on a Martian basalt composition show that DV augite/melt is greater than DV pigeonite/melt in samples equilibrated under the same fO2 conditions. This increase is due to the increased availability of elements for coupled substitution with the V3+ or V4+ ions, namely Al and Na. For this bulk composition, both Al and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V3+ and V4+ are the main V species in the melt at fO2 conditions of IW-1 to IW+3.5, whereas pyroxene grains at IW-1, IW, and IW+1 contain mostly V3+. This confirms the idea that V3+ is more compatible in pyroxene than V4+. The XANES data also indicates that a small percentage of V2+ may exist in melt and pyroxene at IW-1. The similar valence of V in glass and pyroxene at IW-1 suggests that V2+ and V3+ may have similar compatibilities in pyroxene.
    • Validating and Improving Archaeological Phasing at St. Mary Spital, London

      Sidell, Jane; Thomas, Christopher; Baylis, Alex (Department of Geosciences, The University of Arizona, 2007-01-01)
      This paper outlines the radiocarbon program applied to the excavation and skeletal assemblage from the cemetery of the medieval Priory and Hospital of St. Mary Spital in London. Problems encountered in dating medieval cemeteries are outlined. The problems were addressed through the application of Bayesian modeling to validate and refine conventional approaches to constructing phases of archaeological activity. It should be noted that this project was solely funded by the developer of the land; such projects rarely undertake even modest programs of 14C dating. We aim to show how the investment of a proportionally small sum, compared to the overall project costs, may reap significant benefits.
    • Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets

      Pierazzo, E.; Artemieva, N.; Asphaug, E.; Baldwin, E. C.; Cazamias, J.; Coker, R.; Collins, G. S.; Crawford, D. A.; Davison, T.; Elbeshausen, D.; et al. (The Meteoritical Society, 2008-01-01)
      Over the last few decades, rapid improvement of computer capabilities has allowed impact cratering to be modeled with increasing complexity and realism, and has paved the way for a new era of numerical modeling of the impact process, including full, three-dimensional (3D) simulations. When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter-code variability.
    • Validity of 14C Ages of Carbonates in Sediments

      Chen, Yijian; Polach, Henry (American Journal of Science, 1986-01-01)
      This review is based on geologic surveys carried out in Australia and China as well as on more than 300 14C dates published in Radiocarbon. Evaluated are the origins and pathways of carbonate formation, stable isotopic composition, carbonate nodule growth rates and paleo-climatic effects. The three identified delta-13C abundance peaks are unrelated to environment and carbon source whilst 14C ages group themselves into periods corresponding to past humid warm climate. It is concluded that the major error in caliche dating is due to incorporation of old limestone whilst error on nodule dating is related to their slow growth rate. Thus, caliche antedates and nodules postdate the times of their deposition. delta-13C values cannot be used to correct for limestone or atmospheric contamination effects
    • Valle Vidal Opens to the Public

      Hassell, M. J.; Crellin, Jack S. (Society for Range Management, 1985-04-01)
    • Valley's Farm Income Yearly $200 Million

      Halvorson, Robert L. (College of Agriculture, University of Arizona (Tucson, AZ), 1966)
    • The Value of a Financial Record on a Livestock Farm

      Hamilton, Joe (College of Agriculture, University of Arizona (Tucson, AZ), 1927-06)
    • Value of Black Hills Forest Communities to Deer and Cattle

      Kranz, J. J.; Linder, R. L. (Society for Range Management, 1973-07-01)
      Aspen, pine, and mixed aspen-pine communities were studied at three different locations in the Black Hills National Forest of South Dakota from 1968 to 1970. Overstory densities were greatest in pine with a basal area (diameter at breast height) of 180.5 ft2 per acre. Aspen-pine had 133.6 ft2 per acre and aspen 89.5 ft2 per acre. Understory production was inversely related to overstory density with 590 lb/acre air-dried forage in aspen, 415 lb/acre in mixed aspen-pine, and 215 lb/acre in pine. Aspen communities appeared to represent better feeding areas for both deer and cattle than mixed aspen-pine or pine. However, use by white-tailed deer, estimated by pellet group density, was greatest in mixed aspen-pine. Cattle use, estimated by chip density, was greatest in aspen and least in pine.
    • Value of Broom Snakeweed as a Range Condition Indicator

      Jameson, D. A. (Society for Range Management, 1970-07-01)
      Following an initial 13 year stabilization period, changes in broom snakeweed populations on southwestern pinyon-juniper ranges were investigated over a subsequent 13-year period. The changes which occurred appeared to be the result of oscillating populations rather than of range condition.
    • The Value of Egg Laying Contests

      Gibbs, Mack W. (College of Agriculture, University of Arizona (Tucson, AZ), 1925-10)
    • The Value of Government Crop Reports

      Wilson, A. G. (College of Agriculture, University of Arizona (Tucson, AZ), 1927-02)
    • Value of Indian Ricegrass in Range Reseeding

      Verner, J. E. (Society for Range Management, 1956-09-01)
    • Value of mountain rye for suppression of annual bromegrasses on semiarid mined lands

      Andersen, M. R.; Depuit, E. J.; Abernethy, R. H.; Kleinman, L. H. (Society for Range Management, 1992-07-01)
      The value of mountain rye (Secale montanum Guss.) for competitive suppression of 2 annual bromegrasses (downy brome, Bromus tectorum L. and Japanese brome, B. japonicus Thunb) was investigated in a 3-year study on reclaimed coal mined lands in southeastern Montana. Rye established rapidly and vigorously, but did not persist appreciably (either through initially established plants or new seedlings) after the second year. However, mountain rye significantly reduced growth and reproduction of annual bromes during the first 2 growing seasons. Mountain rye also inhibited growth of other concurrently seeded perennial grasses during the first 2 seasons. Annual brome soil seedbanks were not sufficiently reduced in rye-seeded plots to prevent an eventual, third year recovery of brome productivity after a massive dieback of rye between the second and third growing seasons. Mountain rye therefore proved effective for short but not for longer-term control of annual bromes. This study did not allow distinction between the known short-lived nature of mountain rye and/or local environment as causal factors for the massive dieback after the second year.
    • Value of multiple fecal indices for predicting diet quality and intake of steers

      Leite, E. R.; Stuth, J. W. (Society for Range Management, 1990-03-01)
      The relationship of fecal nitrogen fractions and condensed tannins dietary crude protein, in vitro organic matter digestibility, and intake of steers was assessed to determine the suitability of these multiple fecal indices for predicting quality of animal diets under free-roaming conditions. Research was conducted on the Texas A&M Native Plant and Animal Conservancy near College Station, located in the Post Oak Savannah region of Texas. Regression equations were used to evaluate relationships between dietary intake and quality to fecal variables. Dietary crude protein, digestible organic matter, organic matter intake, crude protein intake, and digestible energy intake were determined from previous studies. Corresponding fecal samples were analyzed for absolute output, proportions, and concentrations of nitrogen and selected fractions of fecal organic matter, as well as fecal condensed tannins, proportions of fecal monocot and dicot fragments, and fecal organic matter. In general, no fecal parameter by itself had a high correlation with dietary variables when expressed on a proportion or concentration basis. A combination of fecal indexes accounted for more variation in dietary parameters than fecal nitrogen. Fecal nitrogen fractions did not improve the predictive power of multiple variable models. Equations predicting dietary crude protein (%) and crude protein intake yielded the highest coefficients of determination (R2 = .57 and .51, respectively). Multiple fecal indices used in this study were of limited value in predicting diet quality and intake.
    • Value of Plant Diversity for Diet Mixing and Sequencing in Herbivores

      Provenza, Frederick D.; Villalba, Juan J.; Wiedmeier, Randy W.; Lyman, Tiffanny; Owens, Jake; Lisonbee, Larry; Clemensen, Andrea; Welch, Kevin D.; Gardner, Dale R.; Lee, Stephen T. (Society for Range Management, 2009-02-01)
    • The Value of Tree-Ring Analysis in Engineering

      Lassetter, Roy, 1910- (Tree-Ring Society, 1938-10)
    • Value of Wildland Habitat for Supplying Pollination Services to Californian Agriculture

      Chaplin-Kramer, Rebecca; Tuxen-Bettman, Karin; Kremen, Claire (Society for Range Management, 2011-04-01)
    • Value Shifts in Multiple Use Products from Rangelands

      Quigley, Thomas M. (Society for Range Management, 1989-12-01)
    • Values of Four Communities for Mule Deer on Ranges with Limited Summer Habitat

      Austin, D. D.; Urness, P. J. (Society for Range Management, 1985-03-01)
      Four plant communities were evaluated from May through September for mule deer dietary and nutritional values. The communities were dominated by Utah serviceberry, Gambel oak, big sagebrush, and mixed browse. In early summer deer diets contained many browse and forb species and were high in crude protein, but as summer progressed fewer species were selected and dietary crude protein declined, especially in the big sagebrush and serviceberry communities. Thus late summer was determined the critical period for forage quality. Range conditions were reflected by body size and condition of deer in fall.
    • Values of Range Uses

      martin, William E.; Agricultural Economics (College of Agriculture, University of Arizona (Tucson, AZ), 1981)