• Foraging Ecology And Nutritional Stress Of Tufted Puffins (Fratercula Cirrhata) Inferred From Stable Isotopes, Fatty Acid Signatures, And Field Endocrinology

      Williams, Cory T.; Buck, C. Loren (2008)
      Prey availability has a major impact on the reproductive output of seabirds, yet information on seabird diets throughout the breeding season is often lacking. Although reduced prey availability is known to affect the growth and survival of nestling seabirds, few studies have demonstrated similar effects on indices of adult body condition. I used stable isotopes and fatty acid (FA) signatures to investigate seasonal and age-related variation in the foraging niches of tufted puffins (Fratercula cirrhata). I conducted captive feeding experiments to determine whether inferences based on these techniques are affected by moderate food restriction during growth. I also examined how adult puffins prioritize the competing goals of maximizing the growth rate of their offspring and maintaining their own condition, as measured by body mass and by the stress hormone, corticosterone (CORT). Food restriction during nestling growth affected adipose tissue FA signatures and resulted in blood that was depleted in 15N and 13C relative to well-fed controls. However, effects of nutritional restriction on delta 15N, delta13C, and FA signatures were small compared to variability in prey, indicating physiological effects do not preclude use of these techniques as dietary tracers. Stable isotopes and FA signatures of free-living adults indicated foraging niches changed over the course of the breeding season. Stable isotopes suggest chick-rearing adults and nestlings feed at the same trophic level while FA signatures indicate that parents feed nestlings a diet different from their own. Body mass of adult puffins declined between incubation and chick rearing periods. For females the magnitude of mass decline did not differ between years, whereas for males the decline was greater in the year where young puffins fledged at a lower mass. In a separate analysis, baseline CORT values of adults of both sexes did not differ between years, but were lower than those observed in a separate study area during two consecutive years with low rates of nestling growth and survival. Assuming elevated CORT and reduced body mass impact survival and/or future fecundity, these results suggest the cost of reproduction may be higher for those adults able to fledge young in years characterized by low productivity.
    • Foraging Ecology And Sociality Of Muskoxen In Northwestern Alaska

      Ihl, Claudia; Ruess, Roger; Klein, David (2007)
      I investigated sociality and winter foraging ecology of muskoxen ( Ovibos moschatus) in Cape Krusenstern National Monument, northwestern Alaska. The nutritional value of moss (Hylocomium splendens, Tomenthypnum nitens) for muskoxen was evaluated by incubating moss in rumen-fistulated muskoxen and simulating post-ruminal digestion by incubation in acid-pepsin. Moss was indigestible in muskoxen and gained mass and nitrogen in the rumen. Consequently, high moss consumption during winter may result in net loss of nitrogen from a muskoxen's system. Local and regional differences in moss use by muskoxen and caribou or reindeer (Rangifer tarandus) were investigated in northwestern Alaska in relation to indicators of winter range quality. On muskox winter ranges, increases in fecal moss indicated decreased graminoid cover, harder snow, increased moss cover, and greater animal densities. Higher mobility of caribou than muskoxen during winter limits use of their feces to reflect local forage selection, but fecal moss may indicate caribou winter range quality on a larger, regional scale. Increasing proportions of moss in muskoxen feces may alert wildlife managers to shifts in forage availability due to changing snow conditions. Roles of male and female muskoxen in coordinating group movements were investigated during the snow-free season. Adult females led most activity initiations, foraging-bout movements, and spontaneous group movements. Rutting males actively manipulated female-led movements through herding and blocking. Leaders incurred no costs in terms of lost foraging time. Habitat use by muskoxen shifted from upland habitats in early summer towards lowland sedge meadows during rut. Muskox group sizes decreased from winter to summer to rut. Muskoxen foraging efficiency decreased with group size in spatially unlimited but not in spatially limited habitats. Adult males contributed least to group cohesion, and their presence may contribute to group fission during rut. A conceptual model is presented which discusses how habitat, foraging, social behavior, and predation threat contribute to group sizes, fission and fusion of muskox groups. Results from this study indicate that winter ranges used by muskoxen in Cape Krusenstern may be limiting, which suggests that numbers of muskoxen in this area will likely remain small. Therefore, hunting quotas should be low and limited to males only.
    • Foraging ecology of female Dall's sheep in the Brooks Range, Alaska

      Hansen, Michael Charles (1996)
      Most wild sheep (Ovis) are primarily diurnal. Thus, extreme cold, darkness, and limited quantities of low-quality forage during long winters above the Arctic Circle present a formidable challenge for sheep. Further, summer is particularly short at these high latitudes, providing little time for sheep to accumulate energy reserves for winter. This thesis discusses dietary and behavioral responses of wild sheep to the constraints of Arctic environments. Specifically, I determined diet composition and selection, forage quality, nutrient intake, and activity budgets of adult female Dall's sheep (ewes) (Ovis dalli dalli) near the northern extreme of the range of wild sheep for 2 years and constructed a model of the energy relationships of these animals. Ewes primarily consumed forbs and grasses during summer, and strongly selected forbs over other forages in accordance with the predictions of optimal foraging theory. Diets primarily consisted of grasses in early winter, shifted to sedges in February, and back to grasses in early spring. Shrubs were consistently the least selected class of forage. When the diet was composed of forages with varying digestibility, microhistological analyses not corrected for differential digestibility were biased toward less digestible forage. Winter forage available to Dall's sheep in the northern Brooks Range was low in both digestibility and protein content. In early summer ewes foraged during all hours of the day when sunlight was present for 24 hours. Sheep restricted their foraging almost entirely to daylight hours near the equinoxes, and foraged during all available hours of light, as well as 2.8 hours of the night in December. Daily foraging time varied from 12.9 hours in June to 7.9 hours in December, and, when measured on a daily basis, was positively correlated with average windchill and daylength. Ash-free fecal nitrogen and in vitro digestible dry matter were most highly correlated with activity level on a monthly basis. Energetics modeling indicated that ewes were in a negative energy balance for 6-8 months each winter and lost nearly 30% of their body weight. Duration of the short summer growing period was most important for weight gain, and presence of deep snow determined weight loss in winter.
    • Foraging ecology of yellow-rumped warblers in an Alaskan boreal forest following a spruce beetle outbreak

      Bartecchi Rozell, Kristen (2004-12)
      I examined the foraging ecology of the Yellow-rumped Warbler (Dendroica coronata) several years after an outbreak of spruce beetles (Dendroctonus rufipennis) in the Copper River Basin, Alaska. With increased beetle-induced mortality of white spruce (Picea glauca), a preferred foraging substrate, we predicted warblers would respond through: (1) decreased overall use of white spruce, (2) increased selectivity of live white spruce that remained, and (3) reduced foraging efficiency, reflected by a greater proportion of time spent foraging and lower prey attack rates. We examined warbler foraging behavior and arthropod biomass on commonly used foraging substrates, and in stands with low-moderate (<40%) and heavy (>40%) spruce mortality. Live and dead white spruce, quaking aspen, and willow were the most commonly used foraging substrates, and selection of coniferous versus deciduous tree types varied by breeding stage. Yellow-rumped Warblers foraged extensively on dead spruce in stands with heavy spruce mortality, although they avoided it in stands with low-moderate spruce mortality. Dead spruce supported significantly lower arthropod biomass than any other tree type except black spruce, and warblers that foraged in dead spruce tended to have lower prey attack rates than when they foraged in live white spruce.
    • Foraging patterns of northern fulmars in Alaska inferred from fatty acid signature analysis

      Wang, Shiway W. (2005-12)
      Diets of Northern Fulmars (Fulmarus glacialis) in the North Pacific are poorly known, and thus relationships of fulmars to supporting food webs and their potential sensitivity to ecosystem variability, such as that driven by a changing climate, also are uncertain. I employed a new technique, fatty acid (FA) signature analysis, to examine dietary differences among fulmars at three colonies in Alaska. I predicted that 1) signatures of adipose tissue and stomach oils would differ because the time scale each depot reflects differ and/or because adipose tissue FAs may be influenced by predator metabolism, while stomach oil FAs may be influenced by differential uptake; 2) fulmar diets would differ between colonies located in distinct oceanographic settings, which create unique habitats for prey assemblages; 3) diets would differ temporally within colonies because of inter-annual variability in the physical environment resulting in variation of prey FA signatures; and 4) diets of adult fulmars and their chicks would be similar because they feed by regurgitation. I found that FA signatures of adipose tissue were significantly different than those of stomach oil; there were conspicuous spatial and temporal differences in adipose tissue signatures; but diets of adults may differ from those of chicks.
    • Foraging tactics of humpback whales feeding near salmon hatchery-release sites in Southeast Alaska

      Kosma, Madison M.; McPhee, Megan V.; Straley, Janice M.; Szabo, Andrew R.; Wooller, Matthew J. (2019-12)
      Increases in the humpback whale (Megaptera novaeangliae) population have generated considerable interest in understanding the foraging habits of these large marine predators in the Gulf of Alaska. Globally, humpback whales are classified as generalist predators but are known to exhibit localized differences in diet. Intensified predation pressure is of particular concern to resource managers, who have observed whales feeding at juvenile hatchery salmon release sites in Southeast Alaska. We assessed the diets and behavioral tactics of humpback whales foraging near Hidden Falls Hatchery release sites (in Chatham Strait, 2016 to 2018) to better understand their predatory effects on juvenile hatchery-reared salmon. We used skin biopsies, prey sampling, and stable isotope analysis to estimate whales' diet composition. Aerial footage and photographic sequences were used to assess the foraging tactics used on this prey source. We observed three individual whales repeatedly feeding on juvenile hatchery-reared salmon, and we were able to sample them multiple times over a period spanning shifts in diet. Overall, the diets of these whales were higher trophically than other humpback whales foraging in the area, even before feeding on juvenile hatchery salmon started. These hatchery-feeding whales may be generally more piscivorous than other whales, which focused on planktivorous prey. Our repeat sampling, in conjunction with scheduled introductions of a novel prey source, provided a semi-controlled feeding experiment that allowed for incorporation and turnover rate estimates from humpback whale tissue in a way that was not previously possible for large, free-ranging cetaceans. Finally, during the course of this study we discovered an undescribed feeding tactic employed by hatchery-associated whales. We observed the use of solo bubble-nets to initially corral prey, followed by calculated movements to establish a secondary boundary with the pectoral fins that further condensed prey and increased foraging efficiency. Our study provided the first empirical evidence for what we describe as "pectoral herding". This work deepens our knowledge about humpback whale foraging ecology, how this innovative species is able to exploit newly available prey, and to what extent they feed on commercially valuable hatchery salmon.
    • Forecasting catches of Pacific salmon in commercial fisheries of southeast Alaska

      Marshall, Robert Paul (1992)
      Data collections since 1911 and statistical methods from time series analysis are employed to forecast catches of pink, chum, coho, and sockeye salmon in Southeast Alaska. Knowledge of the spatial and temporal domains favored by Pacific salmon originating in Southeast Alaska is summarized to provide a basis for estimating environmental variation experienced by each species. Catches in northern, southern, and all of Southeast Alaska are forecast with univariate ARIMA, transfer function-noise (TFN), and vector ARMA models. Univariate models for catch in numbers and catch in weight yielded similar results for each species. Air and sea surface temperatures, freshwater discharge, and coastal upwelling enter TFN models for several species and areas. Environmental variables allow TFN models to explain a small amount of variation in the catches (average of 19%) above that explained by univariate models. Forecasts for most, but not all, species and areas are improved (average of 16%) by including environmental data in TFN models. Stock-recruit models with a parameter for density dependent mortality provide the best forecasts of pink salmon catch and are recommended for future forecasts. Winter air and sea surface temperatures enter stock-recruit models for pink salmon, and forecasts of catch and recruitment in northern and southern Southeast Alaska tend to oppose each other and cancel (1981-1985), which suggests that the salmon are caught in areas other than where they originated. Mean absolute percentage error (MAPE) for forecasts of pink salmon catch from stock-recruit models in Southeast Alaska, based on data for 1981-1990, is estimated at 49%, with first, second, and third quartiles of 10%, 23%, and 83%, respectively. Catches of Pacific salmon in Southeast Alaska are significantly correlated and are forecast jointly with good accuracy by vector ARMA models, except when effects believed to result from density dependent mortality are present in the data. Correlations indicate that coho salmon smolts might prey on young pink salmon. Also, recruitment of pink salmon in Southeast Alaska and British Columbia is correlated; regional environmental influences might thus affect catches in both areas. In Southeast Alaska, MAPE for forecasting coho and sockeye salmon catch with time series analysis is about 20%, and about 30% for chum salmon.
    • Forecasting stock-specific upriver migration timing of chinook salmon in the Yukon River

      Mecum, Bryce Douglas; Adkison, Milo D.; Quinn, Terrance J. II; Toshihide, Hamazaki; Mundy, Phillip R. (2016-12)
      Pacific salmon (Oncorhynchus spp.) are an economically and culturally important genus of fishes endemic to the North Pacific. Their sustainable management depends on an understanding of the drivers of their abundance and migration dynamics. In many instances, statistical models are employed to predict abundance and run timing before harvest takes place to more effectively meet management objectives. In this thesis, I created a general-purpose predictive model of run timing that can be applied to many salmon populations. I then applied it to Yukon River Chinook salmon (O. tshawytscha) by generating pre-season predictions of inriver run timing, which I then compared with existing observations of run timing at two upriver locations. Prediction errors were low enough for the model to be useful to management. Models such as the one created in this study represent an objective tool that can be used to reduce subjectivity in fisheries management.
    • Forest biometrics and quantitative analysis of forested ecoystems in coastal Alaska

      Peterson, Randy Louis; Verbyla, David; Liang, Jingjing; Barrett, Tara; Greenberg, Joshua (2014-08)
      Growth and yield models are a mainstay of forestry research and a necessary tool in the forest management decision process. Growth and yield models predict forest population dynamics over time and are an invaluable resource to forest managers making harvest and utilization decisions. At present, there are only a few growth models available for Alaska's coastal forests, all of which are either calibrated with even-aged data or outdated. Yield tables and growth models developed with even-aged data can be useful in even-aged management applications such as clear-cuts; however, these models are not able to predict the outcomes of uneven-aged silvicutural systems. The objective of this thesis is the development of a growth and yield model for coastal Alaska and computer applications to facilitate its use. A density-dependent, distance-independent, size- and species-specific matrix forest growth and yield model is calibrated with data collected on permanent sample plots located throughout coastal Alaska. The resulting growth and yield model enables short- and long-term predictions of stand basal area, volume, and biomass. Model assessment, with a focus on plausibility and accuracy, is evaluated on an independent dataset. Two computer programs (AlaskaPro and fgmod) are developed in conjunction with the new model. These programs can be used by forest researchers and land managers to compare the outcomes of various silvicultural prescriptions.
    • Forest Ecology And Distribution Of Bats In Alaska

      Parker, Doreen Ingrid; Cook, Joseph A.; Klein, David R.; Rexstad, Eric A. (1996)
      This thesis documents distribution of bat species in Alaska and effects of clearcutting on bat activity in temperate rainforests of southeastern Alaska. Occurrence of Myotis lucifugus, M. californicus, M. volans, M. keenii, and Lasionycteris noctivagans is confirmed in southeastern Alaska. I describe new specimens of M. keenii from southeastern Alaska, the first in over 100 years. Myotis lucifugus and Eptesicus fuscus are documented north of 64$\sp\circ$ N latitude. Environmental conditions and geography which influence distribution and latitudinal diversity gradients are discussed. Low bat activity in second-growth forests and clearcuts suggests that these areas provide little summer habitat. Higher activity levels in old-growth and riparian forests suggest these areas are important summer habitat. A change in activity between lactation and post-lactation periods is also noted. Unusual aspects of M. lucifugus ecology in southeastern Alaska are: consumption of spiders; presence of maternity colonies in a temperate rainforest; and intermittent use of hibernacula. <p>
    • Forget Everything

      Richardson, Jean Jolene; Reinhard, John (2003)
      These poems take place in a compromised world. People who have lost their visions of life find themselves on the other side of the crisis, and suddenly the goal is no longer simply to live, but to live authentically. The narrative voice that emerges through this collection is one that struggles to face reality without self-deception, and without comfortable simplifications. The poems themselves are embodiments of faith, because a sincere search for truth implies a belief that whatever the world is, it's worth knowing. <p> Most of these poems are lyrics, struggling to convey one feeling or set of feelings. Other revelations necessary to the narrative and emotional arc of the collection require different forms. A section poem addresses fragmentation; a villanelle embodies obsessive thinking; and prose pieces allow a linking of moments and reasons not possible in other forms, but necessary to the investigation of the material. <p>
    • Formation and optical properties of photochromic silver nanoparticles

      Lee, George Patrick (2005-05)
      Spherical silver nanoparticles may be produced by the reduction of Ag (aq) by borohydride in the presences of citrate. When (phenylphosphinidene) bis-(benzenesulfonic acid) is also present, and the reaction mixture is illuminated, nonspherical Ag nanoparticles are formed. We have discovered that the shape of some Ag nanoparticles can be repeatedly changed by subjecting them to numerous cycles of light and dark. To our knowledge, this has never been reported in the literature. These photo chromic Ag nanoparticles displayed at least two different particle shapes: prismatic and spherical. The difference in morphology could be determined by the color of the solution and by the electronic spectra. The prismatic Ag nanoparticles can be photochemically synthesized in 24hrs and then converted into a spherical form by placing them in the dark for 14hrs. This transformation is accompanied by a blue shift in the visible spectrum. The prismatic particles are reformed by placing them in the light for 4 hrs. This transformation has a red shift in the visible spectrum.
    • The formation of pore ice in coarse grained soils

      Fourie, Walter (2005-12)
      Understanding the formation of pore ice in coarse grained soils is important to geotechnical and geo-environmental projects such as the construction of roads, airstrips and gravel foundations as well as the treatment of contaminated soils in the arctic, sub-arctic, alpine and northern regions. The amount of pore ice present controls the strength characteristics of the soils as well as the flow of fluid through the soil. Tests have been conducted to qualify the impact of gradation, temperature, compaction and initial moisture content on the formation of pore ice in coarse grained soils. The purpose of this study was to prepare a conceptual model of the freezing mechanism in coarse grained soils and to qualify the parameters that influence the ice formation. Results from this study indicate that the presence of fine grained particles in a coarse grained soil greatly impact the depth at which the pore space initially becomes saturated with ice. A conceptual model was developed and its application is shown with regards to the process of thaw weakening in roads and the creation of preferential flow paths in permeable reactive barriers.
    • Formation of solar prominences and eruption of solar magnetic arcade systems

      Choe, Gwang-Son; Lee, Lou-Chuang; Akasofu, Syun-Ichi; Roederer, Juan G.; Swift, Daniel W.; Watkins, Brenton J. (1995)
      Formation and eruption of solar prominences, coronal mass ejections (CMEs) and solar flares are the most magnificent phenomena among solar activities. Observations show that there is an interrelationship among these events and that their manifestation is conditioned by certain common photospheric signatures. One of them is the increase in magnetic shear. In this thesis, the evolution of the solar atmosphere is studied by numerical simulations with photospheric motions as boundary conditions. Firstly, mechanisms of prominence formation are investigated. It is found that prominences can be formed by the development of a thermal instability (1) in a rapidly expanding magnetic arcade, (2) in a magnetic island created by magnetic reconnection or (3) in the current sheet between two bipolar arcades. Secondly, the quasi-static evolution of a magnetic arcade subject to footpoint shearing is studied under the ideal MHD condition. Three distinct evolutionary phases are found, in the last of which a current layer develops and grows indefinitely with the increasing shear. Force-free field solutions are also constructed and compared with dynamic solutions. Finally, resistive evolutions of magnetic arcades are investigated imposing resistivity on the pre-sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnection can take place to create a magnetic island. The effects of different values and spatial patterns of resistivity are studied. With a localized resistivity, most of principal features in solar eruptive processes are reproduced. A comparative study is made between the numerical results and observations.
    • Forming a therapeutic response to adolescent impulsivity

      Hansen, Kira M.; Gifford, Valerie; McMorrow, Samantha; Daku, Mike (2017-05)
      Utilizing a biopsychosocial perspective, this paper addresses the impact, causes, and treatment of adolescent impulsivity. Specifically, the defining features of impulsivity are identified, and the implications that impulsivity has on adolescent criminal behaviors, treatment participation, and quality of life measures are addressed. As a result of this paper's findings, a therapeutic integration of Dialectical Behavior Therapy and working memory training is proposed in order to meet treatment needs that have gone unaddressed, and this integrated model is presented in the form of a group treatment manual.
    • Foster Parent Training for the Delivery of Independent Living Skills

      Alley, Kandy; Renes, Susan L.; Cook, Christine R.; Hutchison, Shayle (2013-12)
      Although training is made available to foster parents when they volunteer to share their homes with children in need, the required ten hours for single parents and fifteen hours for coupled parents does not provide enough training for foster parents who are working with youth preparing for independent living to give them the skills they need to succeed. There are many programs designed for youth, but fewer programs are readily available in Fairbanks, Alaska to teach foster parents how to deliver the skills to the youth. Youth leaving foster care continue to have lower outcomes in education, employment, housing, and fiscal management after exiting foster care than children who were raised in traditional homes. The outcome of this literature review is a pamphlet that will assist agencies in educating the parents of foster youth aging out of the foster care system. It will also provide quick access to resources and learning centers that offer training opportunities for foster parents working with youth preparing for independent living.
    • Fostering leadership in high school female athletes through sports psychology and goal setting

      Kriegmont, Gretchen; Cook, Christine; Wilson, Hilary; Morotti, Allan (2016)
    • Foxes and food subsidies: anthropogenic food use by red and Arctic foxes, and effects on Arctic fox survival, on the Arctic Coastal Plain of Alaska

      Savory, Garrett; O'Brien, Diane; Hunter, Christine; Hueffer, Karsten; Person, Brian (2013-12)
      Food subsidies have the potential to impact wildlife on the Arctic Coastal Plain of Alaska. Red foxes (Vulpes vulpes (L., 1758)) expanded their range into Arctic regions during the 20th century, and the availability of anthropogenic foods may have contributed to their success and persistence in the Arctic. Arctic foxes (Vulpes lagopus (L., 1758)) are also known to forage on anthropogenic foods in Prudhoe Bay and to forage on marine mammals on the sea ice, but it is unknown whether these strategies benefit survival of Arctic foxes. This thesis examined: 1) the importance of anthropogenic foods to the diets of red and Arctic foxes in Prudhoe Bay, and 2) the factors with the greatest effect on Arctic fox survival, including access to food subsidies in Prudhoe Bay and on the sea ice. For the first study, stable isotopes of red and Arctic fox tissues were used to infer late summer, late winter, and lifetime (for red fox only) diets. The contribution of anthropogenic foods to the diets of both species was low in late summer (~10%) but high in late winter (49%, 95% credible interval = 38-57%, of red fox diets and 37%, 95% credible interval = 29-44%, of Arctic fox diets). Estimates of lifetime diet in red foxes revealed high levels of anthropogenic food use, similar to the winter diet. To characterize the extent of competition for food resources, dietary niche overlap was examined between both species by comparing isotopic niche space. Both fox species had little isotopic niche overlap but may have greater overlap between their ecological dietary niches. Availability and consumption of anthropogenic foods by red foxes, particularly in winter, may partially explain their year-round presence in Prudhoe Bay. For the second study, nest survival models and satellite collar data were used to evaluate whether multiple factors affected survival of adult and juvenile foxes. Site and sea ice use had two times more support than the other factors. Three groups of foxes were identified based on capture location and sea ice use, which corresponded to different survival rates: Prudhoe Bay foxes, NPR-A foxes that used sea ice during more than eight 2-week periods during the winter (seven 2-week periods for juveniles), and NPR-A foxes that did not use sea ice. Both adult and juvenile foxes at Prudhoe Bay had modestly higher annual survival rates, 0.50 (90% CI 0.31-0.69) and 0.04 (90% CI 0.0-0.08) respectively, than foxes at NPR-A that did not use sea ice, 0.40 (90% CI 0.18-0.62) and 0.01 (90% CI 0.0-0.04) respectively. NPR-A foxes that used sea ice extensively had the highest survival rates. Food subsidies may have far-reaching effects on red and arctic foxes on the Arctic Coastal Plain of Alaska.
    • Foxtail barley (Hordeum jubatum) control with propoxycarbazone-sodium and fluazifop-p-butyl in three Alaska Native grass species

      Jackson, Brian Earl (2007-08)
      Foxtail barley is one of the most detrimental weeds for the Alaska native grass seed industry. Its control is essential for improving seed production and stand longevity so producers can meet statewide seed demands. The objective of this study was to determine suitable chemical controls of foxtail barley for three different native grass species: 'Nortran' tufted hairgrass (Deschampsia caespitosa L.), 'Gruening' alpine bluegrass (Poa alpina L.), and 'Wainwright' slender wheatgrass (Elymus trachycalus L.) formerly (Agropyron pauciflorum L.). Field and greenhouse experiments were performed to identify selectivity between two herbicide compounds and the crops studied. Foxtail barley was extremely sensitive to both compounds at the 1X rate whereas 'Nortran' tufted hairgrass was tolerant of propoxycarbazone. 'Gruening' alpine bluegrass and 'Wainwright' slender wheatgrass were not tolerant of either compound at the full rate but showed greater tolerance of propoxycarbazone at the 1/2X rate. Propoxycarbazone is a potential tool for foxtail barley control in all three native grass species used for seed production in Alaska.
    • Fracture and shakedown of pavements under repeated traffic loads

      Zhang, Tinggang; Raad, Lutfi; Lee, Jonah H.; Hulsey, J. Leroy; Gislason, Gary A.; Covey, David (1998)
      Under repeated external loads, engineering structures or objects may fail by large plastic deformation or fatigue. Shakedown will occur when the accumulation of plastic deformation ceases under repeated loads; the response of the system is then purely elastic. Fatigue and shakedown have been individually studied for decades and no attempt has been made to couple these two mechanisms in the mechanics analysis. In this study, an attempt is made to couple shakedown and fatigue in pavement mechanics analysis using numerical simulation. The study covers three main areas: fatigue, static shakedown, and kinematic shakedown analysis. A numerical approach to fatigue analysis is proposed based on elastic-plastic fracture mechanics. The amount of the crack growth during each load cycle is determined by using the J-integral curve and $\rm R\sb{-}curve.$ Crack propagation is simulated by shifting the $\rm R\sb{-}curve$ along the crack growth direction. Fatigue life is predicted based on numerically estabiished fatigue equation. The numerical results indicate that the algorithm can be applied to fatigue analyses of different materials. A numerical algorithm based on the finite element method coupled with the nonlinear programming is proposed in static shakedown analysis. In this algorithm, both the inequality and equality constraints are included in the pseudo-objective function. These constraints are normalized by the material yield stress and the reference load, respectively. A multidirectional search algorithm is used in the optimization process. The influence of finite element mesh on shakedown loads is investigated. An algorithm that utilizes eigen-mode to construct the arbitrary admissible plastic deformation path is proposed in kinematic shakedown analysis. This algorithm converts the shakedown theorem into a convex optimization problem and can be solved by using a multidirectional search algorithm. Fatigue behavior of a two-layer full-depth pavement system of asphalt concrete is analyzed using the proposed numerical algorithm. Fatigue crack growth rate is estimated and fatigue life is predicted for the system. Shakedown analyses are also carried out for the same pavement system. The comparison between the shakedown load and the fatigue failure load with respect to the same crack length indicates that the shakedown dominates the response of the pavement system under traffic load.