• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 185
  • 76
  • 35
  • 31
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 447
  • 191
  • 105
  • 61
  • 61
  • 51
  • 45
  • 37
  • 36
  • 35
  • 31
  • 27
  • 27
  • 26
  • 23
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

A general hand method of analysis for tall building structures subject to lateral loads /

Hoenderkamp, Hans J. C. D. January 1983 (has links)
A generalized approximate hand method of analysis is presented for determining the lateral deflections and internal forces in complex multi-storey structures subject to lateral loading. The buildings may include symmetric or asymmetric combinations of coupled walls, rigid frames, shear walls, wall-frames, rigid frames with central walls, frames with single and multi-storey bracing systems as well as cores that are either open or partially closed by floor beams. The deformations taken into account include bending, axial, shear and torsion. / The analysis is based on the continuous medium technique in which the bents in the structure are replaced by idealized assemblies representing their characteristic modes of behaviour. The proposed method is restricted to structures with uniform geometry up the height and linear elastic behaviour of the structural members. / Design equations are presented for the conventional lateral loading cases: a concentrated load at the top of the structure, a uniformly distributed load, and a triangularly distributed load with maximum intensity at the top. The simplicity of this method allows the sway of a structure, the maximum storey sway and its location in the height of the structure to be determined graphically. This procedure enables not only a rapid estimate of the deflections in the structure but together with an assessment of the internal forces it provides a design office method of comparing the efficiencies of different structural alternatives in the preliminary design of tall building structures.
242

EVALUATING A NOVEL ENDOPHYTIC GRASS FOR ITS POTENTIAL TO REDUCE INVERTEBRATE POPULATIONS AND ASSOCIATED BIRD STRIKE RISK AT AIRPORTS

Miller, Diana M 01 January 2015 (has links)
Aircraft strikes are a significant safety hazard on airports worldwide. Wildlife management at airfields is the most effective tactic to reduce airstrike risk – to modify the habitat to be undesirable to animals. Tall fescue grasses containing a fungal symbiont may serve that purpose. They produce alkaloids that convey resistance to some grass-feeding invertebrates, which might in turn reduce incidence of insectivorous birds. A commercial endophytic grass (Avanex™) consisting of ‘Jackal’ tall fescue infected with a unique endophyte (AR 601) is purported to contain especially high levels of alkaloids and to reduce bird populations if planted at airports. I evaluated it against the common KY31 tall fescue with its wild-type endophyte for invertebrate and vertebrate deterrence. Invertebrate abundance, survival, growth, and development were generally similar on Jackal E+ or KY31 E+. Spanish goats and wild birds showed no avoidance of Jackal E+, nor did Jackal E+ contain significantly higher levels of alkaloids than did KY31 E+. The Avanex™ tall fescue was not any better than KY31 in deterring herbivores but the concept is sound. However, better understanding of the relationship between grass, endophyte, alkaloid, and herbivore is needed to inform how such grasses might be used to reduce bird strike hazard.
243

GRAZING EVALUATION OF A NOVEL ENDOPHYTE TALL FESCUE DEVELOPED FOR THE UPPER TRANSITION ZONE

Johnson, Jennifer Michelle 01 January 2010 (has links)
A wild-type endophyte (Neotyphodium coenophialum [(Morgan-Jones & Gams) Glen Bacon & Hanlin]) that infects tall fescue [Lolium arundinaceum (Schreb.) Darbysh. = Schedonorous arundinaceum (Schreb.) Dumort.] imparts tolerances to moisture, heat, and grazing stresses, but also produces ergot alkaloids that adversely affect performance and physiology of cattle. Novel endophytes, developed by AgResearch Ltd. NZ, can sustain fescue persistence and productivity, but do not produce toxic ergot alkaloids. University of Kentucky Plant Breeder, T. D. Phillips Ph.D, developed a tall fescue experimental population (KYFA9301) for the upper transition zone. A 2-yr grazing experiment was conducted with steers to evaluate steer performance and physiology, and forage quality and productivity of KYFA9301 infected with AR584 novel endophyte (AR584) compared with KY31 wild-type endophyte (KY31), endophyte-free KYFA9301 (EF9301) and AR542-‘Jesup’ (MaxQ). Fescue-endophyte combinations were assigned to 1.0-ha pastures in a randomized complete block design with three replications. Pastures were grazed with variable stocking (four testers) from 6 May to 23 July 2008 (76 d), and 2 April to 25 June 2009 (84 d). Shrunk bodyweights were taken at initiation and termination of grazing each year. Average daily gains among MaxQ, AR584, and EF9301 were similar and were greater (P < 0.10) than KY31. Rectal and skin temperatures were collected three times each year at approximately days 28, 56, and study completion, along with blood collection for serum prolactin assay. Rectal and skin temperatures among AR584, MaxQ, and EF9301 were similar and were lower (P < 0.10) than KY31. Serum prolactin concentrations were similar among the three nontoxic varieties and higher (P < 0.10) than KY31. Forage collections were taken at 2 week intervals throughout the study each year and nutritive quality analysis were conducted through wet chemistry to determine forage acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), and In-Vitro Dry Matter Digestibility (IVDMD). Nutritive analyses indicated no differences between fescue-endophyte combinations with the exception of EF9301 having higher ADF concentrations (P = 0.031) than KY31 during the dry year of 2008. Results indicated steer performance and physiological responses for KYFA9301, with and without AR584 were enhanced compared to KY31 and similar to those for MaxQ.
244

RESTORATION OF TALL FESCUE PASTURES TO NATIVE WARM SEASON GRASSLANDS: DOES A FUNGAL ENDOPHYTE SYMBIOSIS PLAY A ROLE IN RESTORATION SUCCESS?

Hall, Sarah Lynn 01 January 2011 (has links)
Tall fescue, a cool-season grass native to Europe, central Asia, and northern Africa, has been widely distributed throughout the U.S. for use as turf and forage. Following its widespread planting, its ability to associate with a toxic fungal endophyte, Neotyphodium coenophialum, was discovered. Research has linked this fescue-endophyte association with increased biotic and abiotic stress resistance in endophyte-infected (E+) versus endophyte-free (E-) plants, and these differences may affect the ability of land managers to eradicate tall fescue and restore native grasslands. I conducted three studies to examine whether E+ tall fescue plants respond differently to management than E- plants, and whether the success of planted native species might be impacted via indirect soil effects. My overall hypotheses were that E+ plants would recover from restoration/eradication efforts better than E- plants, and that E+ fescue would reduce microbial symbionts in the soil needed by planted native species. I first conducted a field study of a tall fescue pasture consisting of four sub-units being restored with different combinations of prescribed burns and/or herbicide applications, as well as an unmanaged control. I found no evidence of E+ plants preferentially surviving restoration management; however this field had unusually low endophyte infection rates to begin with. The second study was a greenhouse experiment in which I measured growth of E+ and E- plants exposed to different watering regimes (wet, dry) and prescribed burn treatments (none, one, or two burns). Watering regime significantly affected all measured growth parameters (wet>dry), but few endophyte effects were found and when present were opposite the hypothesis (E->E+). All burned plants quickly re-grew tiller lengths comparable to the unburned control, with recovery occurring faster following the second burn compared to the first. My final study examined growth and arbuscular mycorrhizal colonization of native species planted by seed into soil from beneath E+ and E- tall fescue. I observed few differences in mycorrhizal colonization or biomass for seedlings between soil from E+ and E- tall fescue. Taken together, my results indicate endophyte status of tall fescue pastures being restored to native grassland species may not be important in governing restoration success.
245

THE INFLUENCE OF TALL FESCUE CULTIVAR AND ENDOPHYTE STATUS ON ROOT EXUDATE CHEMISTRY AND RHIZOSPHERE PROCESSES

Guo, Jingqi 01 January 2014 (has links)
Tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) is a cool-season perennial grass used in pastures throughout the Southeastern United States. The grass can harbor a fungal endophyte (Epichloë coenophiala) thought to provide the plant with enhanced resistance to biotic and abiotic stress. However, the alkaloids produced by the common variety of the endophyte cause severe animal health issues resulting in a considerable amount of research focused on eliminating the toxic class of alkaloids while retaining the positive abiotic and biotic stress tolerance attributes of the other alkaloids. In doing so, very little attention has been paid to the direct influence the fungal-plant symbiosis has on rhizosphere processes. Therefore, my objectives were to study the influence of this relationship on plant biomass production, root exudate composition, and soil biogeochemical processes using tall fescue cultivars PDF and 97TF1 without an endophyte (E-), or infected with the common toxic endophyte (CTE+), or with two novel endophytes (AR542E+, AR584E+). I found that root exudate composition and plant biomass production were influenced by endophyte status, tall fescue cultivar, and the interaction of cultivar and endophyte. Cluster analysis showed that the interaction between endophyte and cultivar results in a unique exudate profile. These interactions had a small but perceptible impact on soil microbial community structure and function with an equally small and perceptible impact on carbon and nitrogen cycling in soils from rhizobox and field sites. These studies represent the first comprehensive analysis of root exudate chemistry from common toxic and novel endophyte infected tall fescue cultivars and can be used to help explain in part the observed changes in C and N cycling and storage in pastures throughout the Southeast U.S..
246

BEEF CATTLE GRAZING PREFERENCE OF TALL FESCUE AS AFFECTED BY ENDOPHYTE

Owens, Herbert Troye, III 01 January 2011 (has links)
Many factors control, contribute to, stimulate and limit forage selection. It is apparent that cattle prefer certain cultivars compared to others. This study sought to test if cattle displayed preferences for certain cultivars over a two-year period in 2008 and 2009. Determining the effect of endophyte status on preference was another objective. Previous research showed rapid increase in the selection of preferred cultivars, i.e., diet learning. We attempted to replicate those results. Forty cultivars (34 tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) cultivars), two festuloliums (Festuca pratensis x Lolium perenne), two meadow fescue (Lolium pratense) and one meadow brome (Bromus biebersteinii), and one orchard grass (Dactylis glomerta L.)) were used to determine preference and to investigate factors contributing to preference. From this two-year study, we observed that cattle preferred certain cultivars compared to others, e.g. KYFA9819 > Latar-OG > Barfest-FL and AU-Triumph < 97TF1-EF < Seine, the most and least preferred cultivars, respectively. During drought conditions, both novel and toxic endophyte cultivars were preferred significantly (P < 0.05) to endophyte free counterparts. The cattle showed rejection of unpalatable grasses but did not clearly show learning to increase selection of desired cultivars.
247

COMPARISON OF ROPE-WICK AND BROADCAST TREATMENTS FOR CONTROL OF CANADA THISTLE AND TALL IRONWEED

Fryman, Daisy M. 01 January 2009 (has links)
Tall ironweed (Vernonia altissima) and Canada thistle (Cirsium arvense) control in cool season grass pastures was evaluated in 2007 and 2008. Tall ironweed was evaluated in Fayette and Boone Counties, KY and Canada thistle was evaluated at Spindletop Research Farm. Herbicides applied selectively with a rope-wick were compared to a broadcast foliar spray. Treatments were a broadcast treatment, of aminopyralid + 2, 4-D and six rope-wick treatments: aminopyralid at three concentrations, glyphosate, triclopyr and clopyralid at one concentration each. The Boone County location had five broadcast foliar treatments: aminopyralid at three rates, triclopyr + fluroxpyr, and 2,4-D + triclopyr. The Canada thistle study consisted of the same six rope-wick treatments as the Fayette County tall ironweed study. A broadcast treatment of aminopyralid at 70 g a.e./ha was included in 2008. Studies were evaluated 1, 2, 3, 4, 8 and 52 weeks after treatment. Aminopyralid plus 2,4-D provided 86% control of tall ironweed 52 WAT. Aminopyralid at 20% v/v controlled 65% of tall ironweed. Canada thistle control 52 WAT ranged from 0 to 25% control for the six ropewick treatments.
248

EFFECT OF DIETARY EXPOSURE TO ERGOT ALKALOIDS ON CONTRACTILITY OF BOVINE MESENTERIC VASCULATURE AND RUMEN MOTILITY

Egert, Amanda M. 01 January 2014 (has links)
Endophyte-infected (E+) tall fescue grass has been associated with fescue toxicosis, a costly syndrome characterized by poor cattle performance and health resulting in significant production losses. The fungal endophyte produces ergot alkaloids, which help the grass thrive in poor conditions but are toxic to mammals. A number of symptoms of fescue toxicosis can be related to vasoconstriction of bovine core, peripheral, and foregut vasculature. The first part of this series of experiments demonstrated ergot alkaloids were also vasoactive in midgut vasculature, with the exception of lysergic acid. Additionally, prior dietary exposure to ergot alkaloids decreased the contractile response of mesenteric vasculature to many of the ergot alkaloids tested. In the second part of this series, a non-invasive method was developed for measuring rumen motility in cannulated cattle. Using this technology without different dietary treatments, it was determined that 8 to 16 h after feeding was the least variable between animals and would provide the best opportunity to measure differences in motility. Application of this technique in the third part of this series investigated the effect of ruminally dosed ergot alkaloids on rumen motility. Treatments were not effective at inducing fescue toxicosis, and no differences in rumen motility variables were detected.
249

Field works: explorations in the tall grass prairie landscape

Wreford, Liz 11 April 2007 (has links)
‘FIELD WORKS’ explores landscape experiences that were once common to the tall grass prairie region of Manitoba. The route through this project winds in and out of urban surfaces to reveal memories embedded in the land. It documents forgotten and dormant prairie events so that they might be woven back into the fabric of the city. The purpose of this project is to transfer explored and speculative experience into a physical route through the urban prairie landscape. It is an effort to expose the layers clinging to physical memories rooted in the prairie.
250

Field works: explorations in the tall grass prairie landscape

Wreford, Liz 11 April 2007 (has links)
‘FIELD WORKS’ explores landscape experiences that were once common to the tall grass prairie region of Manitoba. The route through this project winds in and out of urban surfaces to reveal memories embedded in the land. It documents forgotten and dormant prairie events so that they might be woven back into the fabric of the city. The purpose of this project is to transfer explored and speculative experience into a physical route through the urban prairie landscape. It is an effort to expose the layers clinging to physical memories rooted in the prairie.

Page generated in 0.0697 seconds