Now showing items 2010-2029 of 20709

    • The Baby Beef Experiment

      Scott, E. J.; Department of Animal Husbandry (College of Agriculture, University of Arizona (Tucson, AZ), 1926-01)
    • Back to the Future: Forest Service Rangeland Research and Management

      Mitchell, John E.; Ffolliott, Peter F.; Patton-Mallory, Marcia (Society for Range Management, 2005-06-01)
    • Background Components of a Liquid Scintillation Counter in the 14C Window

      Jonsson, G.; Theodórsson, P. (Department of Geosciences, The University of Arizona, 2007-01-01)
      We present a broad and detailed study of the background components of a liquid scintillation (LS) detector, using a simple laboratory-built system, ICELS. It was specifically designed for radiocarbon dating and is compact and easily transportable (total weight 35 kg). Its flexible LS detector unit has a dome-shaped vial with 3 mL benzene to which 45 mg butyl-PBD is added. The vial sits on the top of a vertical 28-mm-diameter phototube. The gamma radiation, to which the benzene is exposed under varying conditions, was measured by replacing the vial with a 38-mm-diameter NaI crystal. The pulse-height spectra of the 14C LS background and the NaI gamma background were measured in a surface laboratory and in a deep underground counting room with: 1) a lead shield of varying thickness; 2) lead of normal and low 210Pb concentration; 3) phototubes of 2 different types; and 4) varying benzene volume. The beta emission from the face of the tubes was measured with a low-level Geiger counter.
    • Background Concentration of 14C in Aquatic Samples from Brackish Lake Obuchi, Rokkasho, Japan, Adjacent to Nuclear Fuel Reprocessing Facilities

      Ueda, Shinji; Kondo, Kunio; Inaba, Jiro (Department of Geosciences, The University of Arizona, 2007-01-01)
      The brackish Lake Obuchi in Rokkasho, Japan, is adjacent to the first Japanese commercial nuclear fuel reprocessing facilities, which are now undergoing performance testing, with commercial operation scheduled to start in 2007. Preparatory surveys were made by measuring the background levels of radiocarbon for water, aquatic biota, and sediment samples using accelerator mass spectrometry (AMS) in order to study the potential effects of 14C released by the plant to the 14C concentration in aquatic samples. Concentrations of 14C in Futamata River in 2004 ranged from 102 +/- 0.5 to 109 +/- 0.6 pMC (average 106 +/- 0.6 pMC), while 14C concentrations in brackish water from Lake Obuchi and in seawater were 89 +/- 0.5 to 104 +/- 0.4 pMC (average 98 +/- 0.5 pMC) and 82 +/- 0.6 to 102 +/- 0.4 pMC (average 93 +/- 0.5 pMC), respectively. The relationship between 14C concentration and salinity showed a negative correlation (r = 0.68, P < 0.01, n = 20). 14C concentration in selected aquatic biota (i.e. fish, benthos, and seagrass) from 2003 to 2004 ranged from 105 0.7 to 107 0.6 pMC and in zooplankton and phytoplankton was 103 +/- 2.4 to 105 +/- 1.7 pMC. The depth profile of 14C in 3 core sediment samples from Lake Obuchi showed maximum concentrations from 103 +/- 0.5 to 106 +/- 0.5 pMC at 520 cm depth. The vertical profile of 14C concentration in the sediment did not follow global atmospheric 14C fallout. We confirmed that the background level of 14C concentration in aquatic samples in brackish Lake Obuchi before operation of the reprocessing plant was similar to the concentration (~106 pMC) in the recent atmosphere.
    • Background Measurements with Different Shielding and Anticoincidence Systems

      Loosli, H. H.; Forster, Markus; Otlet, R. L. (American Journal of Science, 1986-01-01)
      Extremely low background count rates are a necessary condition for both the measurement of 39Ar concentrations in ground and ocean water and of 14C activities in small samples using gas proportional counting techniques. A systematic comparison of the performance of three different designs of shielding systems in four different installations has been made. Background values of selected gas proportional counters were measured, compared and separated into their various components. Acceptably low backgrounds were obtained in all the systems tried. The performance of a Nail shield in a surface laboratory was found to be at least equal to the best obtained with a gas ariticoincidence detector in a deep underground laboratory.
    • Backyard Water Management

      Ketchum, Lynn (College of Agriculture, University of Arizona (Tucson, AZ), 1988)
    • Bacteria Smuggle Genes Into Tobacco Plants

      College of Agriculture, University of Arizona (Tucson, AZ), 1984-06
    • Bacterial Seed-Piece Decay & Blackleg of Potato

      Stanghellini, Michael E.; Department of Plant Pathology (College of Agriculture, University of Arizona (Tucson, AZ), 1972)
    • Bacteriology of Milk

      Shouse, H. J. (College of Agriculture, University of Arizona (Tucson, AZ), 1925-11)
    • Bad News about the Faire-Construction in French

      Manandise, Daniel; Martin-Callejo-Manandise, Esmeralda (University of Arizona Linguistics Circle (Tucson, Arizona), 1983)
      This paper discusses a select few of the issues related to French causative constructions with faire. Our ambition here is not to propose a new treatment of the phenomenon, but to call attention to "unsifted data" that do not support the "demotion" hypothesis suggested by Carrie (1975, 1976, 1981). We will present evidence that Comrie's general analysis -- established mainly on the basis of canonical constructions such as sentences (1, 2) below-cannot stand unchanged, and needs further refinement, if it is to account adequately for all possible instances of the constructions in question. 2 (1) a. Valéry mange. - 'Valéry eats' b. Francois fait manger Valéry. - 'François makes Valéry eat' (2) a. Valéry mange un escargot. - 'Valéry eats a snail' b. François fait manger un escargot á Valéry. - 'François makes Valéry eat a snail' The (b)-sentences above are instances of the faire-construction, and the (a)-sentences are their non- causative counterparts. These latter may contain various types of predicates: one -place, two-place, and three-place predicates. The causative construction contains an entity faire, which we shall refer to as a "causative marker ", and an infinitival verbal form, which can be followed by postverbal complements. The introduction of a new element--i.e., the CAUSER (François, in (1) and (2)) --is the source of the "unorthodox" position occupied by the CAUSEE (Valéry, in (1) and (2)), which is "pushed" into a "secondary" position after the infinitive verb manger.
    • Badlands on the Brink! Is Wilderness Designation the Answer?

      Olsen, LaDean (Society for Range Management, 1994-10-01)
    • Bahiagrass Regrowth and Physiological Aging

      Sampaio, E. V. S. B.; Beaty, E. R.; Ashley, D. A. (Society for Range Management, 1976-07-01)
      Pensacola Bahiagrass (Paspalum notatum Flugge) grows by adding new phytomers to the terminal ends of vegetative stolons. A new phytomer and its attached leaf is added on average each 7 to 12 days during growth as long as the tiller is vegetative. The new leaf is supplied with energy primarily for the first 2 to 3 days of growth and, from 3 days of age until fully expanded at 12 days, photosynthates are retained by the leaf. After 12 days, exports are made to other sinks in the sheath, stolon, root, and new tillers. An investigation was completed in which (a) shoot growth (leaves) of plants fertilized with 0, 100, or 300 kg/ha of N were measured for length and clipped at the top of the stolon daily or weekly until the stolons died, (b) photosynthesis rate of leaves of different ages was determined, and (c) photosynthesis was correlated with leaf chlorophyll, and N content by weeks. Thirteen weeks of daily or weekly clipping were required to kill the stolons and regrowth amounted to 749 to 850 kg/ha of dry leaves. Total length of shoot regrowth per square meter ranged between 13 to 22 m for the 13 weeks and was negatively related to N application rate. Photosynthesis started dropping after approximately 25 days, but leaf N and chlorophyll contents were relatively stable for the first 45 days. After 45 days of age all three factors declined rapidly until leaf death occurred 60 ± 6 days after initiation. Stolons live much longer than do leaves.
    • Balance and Behavior of Carbon Dioxide at an Urban Forest Inferred from the Isotopic and Meteorological Approaches

      Takahashi, Hiroshi Aoki; Hiyama, Tetsuya; Konohira, Eiichi; Takahashi, Atsuhiro; Yoshida, Naohiro; Nakamura, Toshio (Department of Geosciences, The University of Arizona, 2001-01-01)
      Diurnal variations in δ14C, delta-13C and the concentration of atmospheric carbon dioxide in an urban forest were measured on 9 February 1999 to discriminate and quantify contributions from different CO2 sources. The biogenic CO2 concentration remained relatively constant throughout the day. However, anthropogenic CO2 concentration fluctuated with the atmospheric CO2 concentration, and seemed to be controlled by wind velocity and the amount of exhaust gases from fossil fuel burning. The vertical profiles of anthropogenic, biogenic, and total CO2 showed a constant concentration within forest during daytime because of the large vertical CO2 influx, strong winds, and neutral atmospheric condition. The biogenic contribution at night decreased from the forest floor upwards with a smooth gradient, while the anthropogenic contribution showed a direct mirror because of the location of respective CO2 sources—the vertical gradient of wind velocity and the horizontal CO2 supply
    • Balance of Ration Nutrients and Efficiency of Feed Utilization by Ruminants. A Review.

      McCullough, M. E. (Society for Range Management, 1955-03-01)
    • Balanced Window Method in 14C Liquid Scintillation Counting

      Theodórsson, P.; Ingvarsdottir, S.; Gudjonsson, G. I. (Department of Geosciences, The University of Arizona, 2003-01-01)
      The authors present a detailed theoretical and experimental study of the liquid scintillation balanced counting method, widely used in radiocarbon dating, using a simple, laboratory-made system. A fixed counting window becomes a balanced window when the high voltage is set where the 14C count rate rises to a maximum. Using a measured 14C pulse height spectrum, we have calculated the lower and upper limits for 11 balanced windows of varying width and their respective counting efficiencies. Furthermore, we have studied: (1) theoretically and experimentally, the counting efficiency for up to a +/15% shift in pulse height from the balanced setting, (2), the change in pulse height due to temperature variations, (3), the long-time stability of the system, and (4), a method that allows a quick determination of the balance voltage for individual samples, using the Compton spectrum of 133Ba. The standard deviation for thirty 24-hr measuring periods for a 14C standard (190 Bq) was within the expected statistical error (0.03%).
    • Balanced-Energy Counting Window for Stable Liquid Scintillation Radiocarbon Dating

      Theodórsson, Pall (Department of Geosciences, The University of Arizona, 2011-01-01)
      This paper describes an optimal radiocarbon counting window for liquid scintillation (LS) 14C dating that secures for unquenched as well as for heavily quenched dating samples maximal stability of 14C counting efficiency and theoretically minimal quench correction. In high-precision dating, a balanced counting window with fixed channel limits is frequently used, where about 3% of the highest part of the 14C spectrum is sacrificed for high 14C counting stability. The stability is, however, diminished for quenched samples. Therefore, this window is here replaced by a balanced fixed-energy 14C counting window where the channel limits depend on the quench level. The LS system used must have a linear amplifier and a multichannel analyzer. All samples are measured at a fixed high voltage. For energy calibration and determination of the quench level, the channel number of the middle of the 59.5-keV peak from an external 241Am gamma source is determined before and after measuring each sample. This counting mode is valuable in high-precision dating. It could be widely applied if adapted to systems with a logarithmic amplifier, generally used in LS dating.
    • Balancing Biodiversity and Food Production: A Better Understanding of Wildlife Response to Grazing Will Inform Off-Reserve Conservation on Rangelands

      Neilly, H.; Vanderwal, J.; Schwarzkopf, L. (Society for Range Management, 2016)
      Protected areas are essential, but not sufficient on their own, to conserve biodiversity into the future. Rangelands, used primarily for livestock grazing, have the potential to complement existing reserve systems and be used for "off-reserve" conservation. Success relies on our ability to manage rangelands to simultaneously achieve positive economic outcomes for graziers while maintaining the ecological processes that support biodiversity. However, we argue that research has failed to effectively inform off-reserve conservation strategies, particularly in relation to vertebrate fauna. Most research has focused on the difference in faunal diversity between ungrazed and heavily grazed areas, but faunal responses between these extremes have received less attention. In reality, moderate levels of grazing seem more likely to achieve the ecological, economic and social balance that would be required for successful offreserve conservation on rangelands. Here we review the current knowledge on the impact of grazing by domestic livestock on terrestrial vertebrate fauna in rangelands, highlighting the relative lack of research on the impact of grazing regimes between the extremes. We argue that a more detailed understanding of vertebrate responses to different grazing intensities is required. Furthermore, if the potential for off-reserve conservation on rangelands is to be realized, graziers need management advice based on the integration of ecological, economic, and social data. © 2016 Published by Elsevier Inc. on behalf of The Society for Range Management. All rights reserved.
    • Balancing Livestock Numbers, Feed and Forage on Ranching Units

      Rasmussen, Leroy H. (Society for Range Management, 1958-07-01)
    • Balancing Livestock with Range Forage and Harvested Feed in South Dakota

      Albee, L. (Society for Range Management, 1957-11-01)
    • Barb Goatgrass: A Threat to California Rangelands

      Peters, A.; Johnson, D. E.; George, M. R. (Society for Range Management, 1996-02-01)