Now showing items 3389-3408 of 20719

    • Bulk mineralogical changes of hydrous micrometeorites during heating in the upper atmosphere at temperatures below 1000 °C

      Nozaki, Wataru; Nakamura, Tomoki; Noguchi, Takaaki (The Meteoritical Society, 2006-01-01)
      Small particles 200 micrometers in diameter from the hydrous carbonaceous chondrites Orgueil CI, Murchison CM2, and Tagish Lake were experimentally heated for short durations at subsolidus temperatures under controlled ambient pressures in order to examine the bulk mineralogical changes of hydrous micrometeorites during atmospheric entry. The three primitive meteorites consist mainly of various phyllosilicates and carbonates that are subject to decomposition at low temperatures, and thus the brief heating up to 1000 degrees C drastically changed the mineralogy. Changes included shrinkage of interlayer spacing of saponite due to loss of molecular water at 400-600 degrees C, serpentine and saponite decomposition to amorphous phases at 600 and 700 degrees C, respectively, decomposition of Mg- Fe carbonate at 600 degrees C, recrystallization of secondary olivine and Fe oxide or metal at 700-800 degrees C, and recrystallization of secondary low-Ca pyroxene at 800 degrees C. The ambient atmospheric pressures controlled species of secondary Fe phase: taenite at pressures lower than 10^(-2) torr, magnesiowstite from 10^(-3) to 10^(-1) torr, and magnetite from 10^(-2) to 1 torr. The abundance of secondary low-Ca pyroxene increases in the order of Murchison, Orgueil, and Tagish Lake, and the order corresponds to saponite abundance in samples prior to heating. Mineralogy of the three unmelted micrometeorites F96CI024, kw740052, and kw740054 were investigated in detail in order to estimate heating conditions. The results showed that they might have come from different parental objects, carbonaterich Tagish Lake type, carbonate-poor Tagish Lake or CI type, and CM type, respectively, and experienced different peak temperatures, 600, 700, and 800~900 degrees C, respectively, at 60-80 km altitude upon atmospheric entry.
    • Bulk mineralogy and three-dimensional structures of individual Stardust particles deduced from synchrotron X-ray diffraction and microtomography analysis

      Nakamura, T.; Tsuchiyama, A.; Akaki, T.; Uesugi, K.; Nakano, T.; Takeuchi, A.; Suzuki, Y.; Noguchi, T. (The Meteoritical Society, 2008-01-01)
      During preliminary examination of particles released from 81P/Wild 2 short-period comet, we analyzed 28 particles by nondestructive means, high-sensitive X-ray diffraction and high-resolution X-ray tomography, in order to characterize bulk mineralogy and three-dimensional structures of individual particles. The analyses were performed at synchrotron facilities, KEK and SPring-8 in Japan. Twenty-eight particles from 5 to 25 micrometers in size, including 25 particles from Track 35 and 3 particles from Track 44, were first analyzed by X-ray diffraction and then 4 out of 28 particles were analyzed by X-ray tomography. All particles are classified into two groups based on silicate crystallinity: crystalline type and amorphous-rich type. The abundance of the former is approximately 10% of the particles investigated. Crystalline type shows very sharp reflections of olivine and low-Ca pyroxene, while amorphous-rich type shows no or very weak silicate reflections, suggesting that silicates are mostly amorphous. Broad reflections of Fe sulfides and Fe silicides are detected from most of amorphous-rich type particles. Subsequent tomography analysis revealed that the crystalline type is non-porous material consisting of coarse silicate crystals larger than 1 micrometer in size, while the amorphous-rich type is very porous aggregates with amorphous silicates and small Fe sulfide and Fe metallic grains. All characteristics of amorphousrich type particles indicate that most of them are melted and rapidly solidified during capture in the silica aerogel. On the other hand, the crystalline type is indigenous cometary particle formed through high-temperature heating episodes that have taken place prior to formation of comet Wild 2. One of the crystalline-type particles (C2054,0,35,6,0) consists of Mg-rich olivine, pyroxene, and kamacite and exhibits porphyritic or poikilitic texture very similar to chondrules.
    • Bunchgrass basal area affects selection of plants by cattle

      Ganskopp, D.; Rose, J. (Society for Range Management, 1992-11-01)
      Cattle are selective foragers in response to several plant attributes. We tested hypotheses that caespitose plants of various basal areas were equally susceptible to herbivory and were defoliated with equal intensity by cattle. Five-hundred crested wheatgrass (Agropryon desertorum (Fischer ex Link) Schultes) plants, distributed among 10 basal area classes, were monitored for frequency and level of utilization after approximately 74% of all plants in pastures were grazed by cattle. Plants with < 25-cm2 basal area were less likely, and plants between 65 and 105-cm2 more likely to be grazed than other classes. Ninety-one percent of the 65 to 85-cm2 basal area plants were defoliated, while only 48% of those < 2 .5 cm2 were grazed. The fact that mid-size plants occurred least often but were defoliated most often lends further credence to the selective grazing hypothesis. Less frequent use by cattle of plants < 2 5-cm2 basal area may enhance chances of seedling establishment and survival of smaller established plants or remnants of deteriorating tufts. Among grazed plants, however, smaller plants endured higher utilization by weight than the overall population. Utilization was equal among other size classes. Because forage yield per unit of basal area declined as plant size increased, cattle probably forage most efficiently by selecting bite-size plants. Researchers using single plants, tiller, or leaves as experimental units should note that varying sized tufts are not equally likely to be defoliated, and plants less than 25-cm2 basal area may receive greater than average levels of utilization from free-ranging cattle under light to moderate utilization levels. These aspects of livestock grazing behavior and research objectives should be considered in selection of experimental units.
    • Bunchgrass Form Classes for Trend Studies

      Cole, G. F.; Wilkins, B. T. (Society for Range Management, 1958-03-01)
    • "Bunny Lady" is Self-Taught Expert

      Quinn, Dale (College of Agriculture, University of Arizona (Tucson, AZ), 2006)
    • Buried Ancient Forest and Implications for Paleoclimate since the Mid-Holocene in South China

      Shen, C. D.; Ding, P.; Wang, N.; Yi, W. X.; Ding, X. F.; Fu, D. P.; Liu, K. X.; Zhou, L. P. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The historical evolution of an ancient forest that developed at Gaoyao, south China, can be divided into 4 stages of radiocarbon intervals (1.1-1.5, 2.0-3.5, 3.6-4.0, and 4.3-4.9 ka) in which the last 3 stages all developed in a wetland and formed humic layers of 2.0, 0.5, and 0.7 m depth, respectively. The humic layers were interrupted by 2 white-gray silty clay layers that most likely formed during climate fluctuations. Four drought events were identified during the evolution of the ancient forest, occurring around 4.3, 3.6, 2.0, and 1.1 ka, respectively, with durations of ~1000 14C yr. These events are consistent with other records both in low- and high-latitude areas, in particular with the little ice ages occurring since the mid-Holocene. Precipitation likely increased from 5.0 to 3.6 ka in south China, then decreased, which is probably the main cause for the development as well as the demise of the ancient forest.
    • Buried Wood from Fairbanks, Alaska

      Giddings, J. L., Jr. (Tree-Ring Society, 1938-04)
    • Buried, Viable Seeds and Their Relation to Revegetation after Surface Mining

      Iverson, Louis R.; Wali, Mohan K. (Society for Range Management, 1982-09-01)
      The quantity and quality of seeds present in prairie soils prior to surface mining were determined in this study. Samples were collected near Beulah in western North Dakota from 4 sites (1 each from grazed and ungrazed areas, 1-year old stockpiled topsoil, and a fresh stockpile). Samples were taken from 3 depths and allowed to germinate in a growth chamber for 16 months. The grazed site had a seed density of over 7,700 seeds m2 (43% were from weed species), and the ungrazed site had 3,900 seeds m-2 (7% were weeds); the stockpiled topsoils had very low seed densities. Seed density and diversity decreased with depth on both the grazed and ungrazed sites; this was especially true for the grazed site where 94% of the seeds were found in the top 7.5 cm. Comparisons were made between the seed banks and the aboveground vegetation of the unmined site and 4 mined sites (ages 1-4 years after reclamation). Analysis indicated that seeds of the most prevalent colonizers after reclamation [e.g. summer cypress (Kochia scoparia), green pigeongrass (Setaria viridis), and Russian thistle (Salsola collina)] were not present in the topsoil; rather, they immigrated from the surrounding areas. Several species which were present in the seed bank [e.g. rough penny royal (Hedeoma hispida), buck-horn (Plantago patagonica), white sage (Artemisia ludoviciana), fringed sage (A. frigida), and wormwood (A. absinthium)] were found in the aboveground vegetation of 3- and 4-year-old mined sites, and at the unmined site. Evidence from seed banks and extant aboveground vegetation suggests that both seed dispersal in time (dormancy) and dispersal in space (immigration) are important in determining the type of vegetation on mined areas after topsoil has been replaced.
    • Burmese Sandhi-Voicing: From the Perspective of Emergent Phonology

      Ni, Tianyi; The Ohio State University (University of Arizona Linguistics Circle, 2022)
      This paper deals with sandhi-voicing in Modern Burmese from the perspective of Emergent Grammar (EG). Sandhi-voicing is only found in compounds, but not all of them. EG predicts that Burmese speakers tend to store compounds with sandhi-voicing as a combination of two morphemes, while those without sandhi-voicing as a whole.
    • Burn-Chop-Rest on Flatwoods/Bluestem Range

      Hendricks, R. Gregory (Society for Range Management, 1983-02-01)
    • Burning Affects Water Intake Of Forest Soil

      Zwolinski, Malcolm J.; Department of Watershed Management (College of Agriculture, University of Arizona (Tucson, AZ), 1965)
    • Burning and 2,4,5-T Application on Mortality and Carbohydrate Reserves in Saw-Palmetto

      Kalmbacher, R. S.; Boote, K. J.; Martin, F. G. (Society for Range Management, 1983-01-01)
      On the flatwoods of the southeastern United States control of saw-palmetto (Serenca repens (Bartr.) Small) is an important step in the improvement of native pastures. This study, conducted at the Ona Agricultural Research Center in south Florida, measured fluctuations in total available carbohydrates (TAC) in rhizomes of burned and unburned saw-palmetto which received a June or October application of 8.9 kg/ha (acid equiv.) of 2,4,5-T. Palmetto kill, change in palmetto cover, and grass canopy cover were evaluated. Burning reduced TAC concentration in rhizomes from 48.8% in March to 14.3% in July as compared to a drop from 47.2% to 37.4% for unburned plants. Applying 2,4,5-T caused a further significant decline in TAC concentration. Both burning and 2,4,5-T resulted in lower rhizome percent dry matter indicating that treatment stress caused metabolism of carbohydrate which was replaced by water. After 1 year there was higher mortality on palmetto receiving 2,4,5-T in June, but after 2 years there was no difference in mortality between June (48%) and October sprayed (39%) plants. Burning was not found to have a significant effect on mortality of sprayed plants. Burning and 2,4,5-T decreased palmetto cover, and burned plants treated with 2,4,5-T in June had less cover than burned plants treated in October with 2,4,5-T. Burning followed by 2,4,5-T application in June increased grass cover from 29.4% at the beginning of the study to 67.5% at the end.
    • Burning and Fertilization for Range Improvement in Central Oklahoma

      Graves, J. E.; McMurphy, W. E. (Society for Range Management, 1969-05-01)
      Controlled burning with combinations of nitrogen, phosphorus, and potassium fertilizer were evaluated for improving a poor condition range. After two annual burns the botanical composition was improved. Reduction of prairie threeawn and rapid recovery of decreaser species were the most obvious improvement factors. Fertilization did not contribute to the speed of recovery. Nitrogen fertilizer produced in excess of 36 lb of forage for each pound of nitrogen applied to the burned plots. Phosphorus produced a significant forage yield increase in 1967 but potassium was not effective in changing forage yield or species composition. Range containing much low quality vegetation should not be fertilized.
    • Burning and Grazing Florida Flatwoods

      Sievers, Ed (Society for Range Management, 1985-10-01)
    • Burning and Grazing Increase Herbage on Slender Bluestem Range

      Duvall, V. L. (Society for Range Management, 1962-01-01)
    • Burning Bluestem Range

      Anderson, K. L.; Smith, E. F.; Owensby, C. E. (Society for Range Management, 1970-03-01)
      The effect of time of burning on weight gains of steers, botanical composition, herbage yield, and soil moisture relations were investigated over seventeen years. Time of burning in relation to period of growth was important in the reaction of individual species. Cool-season species were reduced by spring burning and the desirable warm-season species were favored. Fire also favored some weedy species which had phenology similar to the desirable warm-season grasses. Herbage yields were reduced by early and mid spring burning but remained the same as unburned when late spring burning was applied. Gains on steers were greatest under mid and late spring burning and least under no burning and early spring burning. Higher gains on steers mid and late spring burned pastures came early in the growing season.
    • Burning Costs in Oklahoma Rangelands

      Engle, David M. (Society for Range Management, 1988-06-01)
    • Burning Flint Hills Range

      McMurphy, W. E.; Anderson, K. L. (Society for Range Management, 1965-09-01)
      Late spring burning on May 1 was less detrimental than burning in fall or in early or mid-spring. Late spring burning, however, reduced infiltration rate, soil moisture, and forage yield, as compared with unburned range. Advantages of late spring burning over not burning were an increase in big bluestem, control of Kentucky bluegrass and other less desirable plants, and more rapid beef gains.
    • Burning in a Bunchgrass/Sagebrush Community: The Southern Interior Of B.C. and Northwestern U.S. Compared

      Johnson, A. H.; Strang, R. M. (Society for Range Management, 1983-09-01)
      Investigations following a wildfire near Kamloops, B.C., indicated that, contrary to reported experiences in the United States, gray rabbitbrush (Chrysothamnus nauseosus) is susceptible to fire in this area. Hence caution is necessary when developing burning prescriptions and using extrapolated information.
    • Burning of Northern Mixed Prairie During Drought

      Engle, D. M.; Bultsma, P. M. (Society for Range Management, 1984-09-01)
      Standing crop of current year's growth and response of key management species were evaluated following burning in mid-May (before emergence of warm-season grasses) and mid-June (after emergence of warm-season grasses). The study was conducted during 2 dry years in a mesic Mixed Prairie in South Dakota. Cool-season precipitation was 33% below average in both years of the study, while warm-season precipitation was only slightly below average both years. Standing crop of current year's growth was increased by burning on overflow range sites, but not on silty range sites. Big bluestem (Andropogon gerardi) standing crop was greatest with mid-May burning. Kentucky bluegrass (Poa pratensis) standing crop and leaf length were reduced with burning on both dates. Leaf length, basal area and number of inflorescences of native cool-season grasses were also reduced. Mid-May burning in drought years may be recommended for the reduction of Kentucky bluegrass. However, reductions in production of native cool-season vegetation can be expected on silty range sites. In contrast, mid-June burning in dry years is not recommended.