Now showing items 13999-14018 of 20709

    • Rabbits as a Tool in Pasture and Range Utilization Research

      Hedrick, D. W. (Society for Range Management, 1957-07-01)
    • Rabies in Arizona

      Reed, Raymond E.; Department of Animal Pathology (College of Agriculture, University of Arizona (Tucson, AZ), 1964)
    • Rabies in Rangeland Environments

      Young, James A. (Society for Range Management, 1984-04-01)
    • Race Track Industry Program Grads Get Jobs

      Gonzalez, Julieta (College of Agriculture, University of Arizona (Tucson, AZ), 2005)
    • Radar observations of asteroid 1999 JM8

      Benner, Lance A. M.; Ostro, Steven J.; Nolan, Michael C.; Margot, Jean-Luc; Giorgini, Jon D.; Hudson, R. Scott; Jurgens, Raymond F.; Slade, Martin A.; Howell, Ellen S.; Campbell, Donald B.; et al. (The Meteoritical Society, 2002-01-01)
      We report results of delay-Doppler observations of 1999 JM8 with the Goldstone 8560 MHz (3.5 cm) and Arecibo 2380 MHz (13 cm) radars over 18 days in July-August 1999. The images place thousands of pixels on the asteroid and achieve range resolutions as fine as 15 m/pixel. The images reveal an asymmetric, irregularly shaped object with a typical overall dimension within 20% of 7 km. If we assume that 1999 JM8's effective diameter is 7 km, then the absolute magnitude, 15.15, and the average Goldstone radar cross section, 2.49 km^2, correspond to optical and radar albedos of 0.02 and 0.06, establishing that 1999 JM8 is a dark object at optical and radar wavelengths. The asteroid is in a non-principal axis spin state that, although not yet well determined, has a dominant periodicity of ~7 days. However, images obtained between July 31 and August 9 show apparent regular rotation of features from day to day, suggesting that the rotation state is not far from principal axis rotation. 1999 JM8 has regions of pronounced topographic relief, prominent facets several kilometers in extent, numerous crater-like features between ~100 m and 1.5 km in diameter, and features whose structural nature is peculiar. Arecibo images provide the strongest evidence to date for a circular polarization ratio feature on any asteroid. Combined optical and radar observations from April 1990 to December 2000 permit computation of planetary close approach times to within 10 days over the interval from 293 to at least 2907, one of the longest spans for any potentially hazardous asteroid. Integration of the orbit into the past and future shows close approaches to Earth, Mars, Ceres, and Vesta, but the probability of the object impacting Earth is zero for at least the next nine centuries.
    • Radar observations of asteroid 25143 Itokawa (1998 SF36)

      Ostro, S. J.; Benner, L. A. M.; Nolan, M. C.; Magri, C.; Giorgini, J. D.; Scheeres, D. J.; Broschart, S. B.; Kaasalainen, M.; Vokrouhlicky, D.; Chesley, S. R.; et al. (The Meteoritical Society, 2004-01-01)
      We observed 25143 Itokawa, the target of Japans Hayabusa (MUSES-C) sample-return mission, during its 2001 close approach at Arecibo on twelve dates during March 18-April 9 and at Goldstone on nine dates during March 20-April 2. We obtained delay-Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawas average circular polarization ratio at 13 cm, 0.26 +/- 0.04, is comparable to that of Eros, so its cm-to-m surface roughness probably is comparable to that on Eros. Itokawas radar reflectivity and polarization properties indicate a near-surface bulk density within 20% of 2.5 g cm^(-3). We present a preliminary estimate of Itokawas shape, reconstructed from images with rather limited rotation-phase coverage, using the method of Hudson (1993) and assuming the lightcurve-derived spin period (12 +/-.132 hr) and pole direction (ecliptic long., lat. = 355 degrees, -84 degrees) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 x 312 x 276 m +/- 10%. Itokawas topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9 degrees and everywhere are less than 27 degrees. The radar-refined orbit allows accurate identification of Itokawas close planetary approaches through 2170. If radar ranging planned for Itokawas 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroids orbit.
    • Radar observations of Itokawa in 2004 and improved shape estimation

      Ostro, Steven J.; Benner, Lance A. M.; Magri, Christopher; Giorgini, Jon D.; Rose, Randy; Jurgens, Raymond F.; Yeomans, Donald K.; Hine, Alice A.; Nolan, Michael C.; Scheeres, Daniel J.; et al. (The Meteoritical Society, 2005-01-01)
      We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude-latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001-2004 data to refine that papers constraints on Itokawas shape. The 2004 images, the first of the asteroids southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 x 320 x 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three-dimensional models of the object.
    • Radial Growth of Oak and Aspen Near a Coal-Fired Station, Manitoba, Canada

      Boone, Rachel; Tardis, Jacques; Westwood, Richard; Centre for Forest Interdisciplinary Research (C-FIR), University of Winnipeg, Winnipeg, Manitoba, Canada R3B 2E9 (Tree-Ring Society, 2004)
      Eighteen stands of bur oak (Quercus macrocarpa Michx.) and trembling aspen (Populus tremuloides Michx.) were sampled and analyzed using dendrochronological methods to study the potential effects on tree growth of emissions from a 132 MW coal-fired generating station. Sixteen stands were sampled within a 16-km radius of the station, and two control stands were sampled outside of the range of influence, at distances . 40 km. All stands showed similar radial growth patterns from 1960-2001, regardless of distance from or direction relative to the generating station, and a number of stands, including the controls, had below average growth after 1970. Both species were significantly affected by climatic factors, showing decreased radial growth with increasing June temperature. The species differed in their growth responses to spring precipitation and temperature in the previous October. One bur oak site displayed marked radial growth decline beginning in the mid-1970s, strongly pronounced following 1977. This decline does not appear to be related to emissions from the station, but is suspected to be a result of poor site conditions (shallow soil developed over calcareous till), confounded by a change in drainage (a road was built adjacent to the stand in 1977, perpendicular to the direction of drainage). The below average growth seen in 1970-2001 across most stands is likely attributable to stand dynamics and age effects.
    • Radial pastures: Good Grass Mileage

      College of Agriculture, University of Arizona (Tucson, AZ), 1983-09
    • Radial transport in the solar nebula: Implications for moderately volatile element depletions in chondritic meteorites

      Ciesla, Fred J. (The Meteoritical Society, 2008-01-01)
      In this paper, we explore the possibility that the moderately volatile element depletions observed in chondritic meteorites are the result of planetesimals accreting in a solar nebula that cooled from an initially hot state (temperatures >1350 K out to ~2-4 AU). A model is developed to track the chemical inventory of planetesimals that accrete in a viscously evolving protoplanetary disk, accounting for the redistribution of solids and vapor by advection, diffusion, and gas drag. It is found that depletion trends similar to those observed in the chondritic meteorites can be reproduced for a small range of model parameters. However, the necessary range of parameters is inconsistent with observations of disks around young stars and other constraints on meteorite parent body formation. Thus, counter to previous work, it is concluded that the global scale evolution of the solar nebula is not the cause for the observed depletion trends. Instead, it appears that localized processing must be considered.
    • Radiant Temperatures of Hair Surfaces

      Moen, Aaron N. (Society for Range Management, 1974-09-01)
      The radiant temperatures T(r) of the surfaces of winter pelage of white-tailed deer, mule deer, snowshoe hare, cottontail rabbit, and red fox decrease with a decrease in air temperature T(a) and an increase in wind velocity (U). The relationship between T(r) and T a is linear, but nonlinear for T(r):U. Changes in the lower velocities have a relatively greater effect than changes in the higher velocities. The variation between species results in considerable overlap; the use of thermal scanning techniques for censusing of these different species is doubtful under most field conditions.
    • Radio on the Farm

      McInnes, John W. (College of Agriculture, University of Arizona (Tucson, AZ), 1926-02)
    • Radioactive Graphite Dispersion in the Environment in the Vicinity of the Chernobyl Nuclear Power Plant

      Buzinny, Michael (Department of Geosciences, The University of Arizona, 2006-01-01)
      This paper estimates the radioactive graphite dispersion on the land surface (forest litter and soil) as a result of the Chernobyl Nuclear Power Plant (NPP) release. Graphite mass was calculated using an estimated average concentration of 2.5 x 10^7 Bq/kg C (carbon). The sample collection method, sample origin and its mass, and sample preparation procedure used for preparation of benzene were taken into account to obtain the optimum sensitivity of the method. Thus, the sensitivity of the corresponding method for graphite detection in forest litter was estimated to be 0.2 mg/m2. All analyses gave a range of deposited graphite from 0.12 to 52.6 mg/m2. The maximum value was observed at a site located 9 km west of the Chernobyl NPP. The results of the study indicate the importance of studying the upper layer of soil (05 cm) in addition to the lower layer of forest litter.
    • Radiocarbon 1993 Price List

      Department of Geosciences, The University of Arizona, 1993-01-01
    • Radiocarbon 1994 Price List

      Department of Geosciences, The University of Arizona, 1993-01-01
    • Radiocarbon 1994 Price List

      Department of Geosciences, The University of Arizona, 1994-01-01
    • Radiocarbon Accelerator (AMS) Dates for the Epipaleolithic Settlement at Abu Hureyra, Syria

      Moore, A. M. T.; Gowlett, J. A. J.; Hedges, R. E. M.; Hillman, G. C.; Legge, A. J.; Rowley-Conwy, P. A. (American Journal of Science, 1986-01-01)
      The prehistoric settlement of Abu Hureyra in Syria was occupied in both the Epipaleolithic and Neolithic periods. It has provided significant evidence for changes in economy at the time of the inception of agriculture in southwest Asia. Twenty accelerator mass spectrometry (AMS) dates have been obtained to determine the duration of occupation of the Epipaleolithic settlement there and the precise age of samples of cereal grains and animal bones found within it. The results have demonstrated that the AMS technique can answer such questions because it dates exceedingly small samples with high precision. The dates indicate that the Epipaleolithic settlement was inhabited for about a millennium, from before 11,000 to nearly 10,000 BP, significantly longer than had been anticipated from study of the artifacts.
    • Radiocarbon Activity Measurements of Oolitic Sediments from the Persian Gulf

      Šilar, Jan (American Journal of Science, 1980-01-01)
      Radiocarbon activity of successive parts of Pleistocene and Holocene ooids and mollusk shells from the Persian Gulf, Kuwait, was measured. The inner part of the ooids showed the lowest activity and the cement between grains the highest. Radiocarbon activities correspond to the general stratigraphy and to the position of the sediments. Radiocarbon ages of Pleistocene sediments seem to be very low due to recrystallization of aragonite. Higher radiocarbon activity of cement indicates that atmospheric carbon dioxide was involved in the subaerial diagenetic process. The radiocarbon age of well-preserved mollusk shells seems to be lower than their allegedly Pleistocene geologic age.
    • Radiocarbon Activity Variation in Dated Tree Rings Grown in Mackenzie Delta

      Fan, C. Y.; Tie-Mei, Chen; Si-Xun, Y.; Kai-Mei, Dai (American Journal of Science, 1986-01-01)
      We measured the Delta-14C values in 57 rings (from AD 1824 to 1880) of a white spruce grown in Mackenzie Delta (68 degrees N, 130 degrees W), as part of our continuing study of the Delta-14C variation related to solar activities. The values exhibit a 10 per mil fluctuation with an 11-year periodicity anti-correlated with the solar activity cycle. We also measured the Delta-14C values in 6 rings (from AD 1940 to 1945). The abnormally high value in the 1943 ring may be due to two large solar flares occurring in 1942.
    • Radiocarbon Activity Variation in Dated Tree Rings Grown in Mackenzie Delta

      Fan, C. Y.; Tie-Mei, Chen; Si-Xun, Yun; Kai-Mei, Dai (American Journal of Science, 1983-01-01)
      Forty-five tree rings (1881-1925) were taken from a white spruce grown near Campbell River in Mackenzie Delta, Canada, for the measurement of 14C activity variation. Because of the narrowness of the rings, 2 and sometimes 3 rings were combined to yield a total of 21 specimens. The 14C content in these specimens was measured with a liquid scintillation-PM tube counter system of the History Department of Peking University. The data points exhibit a 10 per mil variation, anti-correlated with sunspot numbers. The physical implication is discussed.