• Rivers From The Air

      Odden, Mary Elaine; Soos, Frank; Bartlett, D. A.; Morgan, John (1995)
      This is a collection of creative non-fiction essays. They are triggered by events and persons from my life's experiences, but I hope they shed light on experiences I share with others: coming of age, mothering, probing relationships with nature, understanding and misunderstanding strangers and friends. The Anglo-Saxons believed that to see something was to cast a shaping light upon it, rather than passively accepting what "is." I like that, and it follows, for me, that writing is an active kind of seeing that casts itself in stone here and there like children playing "statues." The whole thing is moving and changing, of course, and can't really be seen. But trying to see it is my idea of what we are here for. <p>
    • Robust control of geared and direct-drive robotic manipulators under parameter and model uncertainties

      Suravaram, Praveen Reddy; Bogosyan, Seta; Sonwalkar, Vikas; Aspnes, John (2005-05)
      The major contribution of this thesis is the design and evaluation of a chattering-free sliding mode controller (SMC), which is a novel application for 2 degree-of-freedom (DOF) planar robot arms exposed to load variations. The performance of the SMC is evaluated in comparison to a proportional-derivative-plus (PD+) controller, as an example of nonlinear model-based controllers, as well as classical linear controllers, such as proportional-derivative (PD) and proportional-integral-derivative (PID). The performance of all four methods has been tested via realistic and detailed simulation models developed for both geared and direct-drive type 2-DOF planar robot arms. The model used in simulations reflects the dynamics of the arm, as well as the actuator dynamics and pulse width modulation (PWM) switching of the power converters. Simulations are performed under unknown load variations for both step and sinusoidal type reference joint trajectories. The results demonstrate that the chattering-free SMC provides increased accuracy and robustness than that of the other controllers and requires no prior knowledge of the system dynamic model and the load variation that the end-effector is subjected to. The results obtained could be extended to the control of a variety of geared and direct-drive type robotic configurations.
    • Rock and age relationships within the Talkeetna forearc subduction complex in the Nelchina area, Southern Alaska

      Barefoot, John D.; Nadin, Elisabeth; Newberry, Rainer; Keskinen, Mary; McCarthy, Paul (2018-12)
      Subduction-zone processes are challenging to study because of the rarity of good exposures and the complexity of rock relationships within accretionary prisms. In south-central Alaska, a remarkably well-preserved exposure of subduction-related outcrops is located at the foot of Nelchina Glacier. Here, the crystalline basement of the Talkeetna volcanic arc is in contact with the mélange of its associated accretionary complex along the Border Ranges fault. A new zircon U-Pb age of an amphibolite from the Talkeetna arc mid-crustal basement just north of the fault is 188.9 ± 2.2 Ma, coincident with previously published dates from the mafic section of the arc. A new amphibole ⁴⁰Ar/³⁹Ar age from the same outcrop yields a plateau age of 182.6 ± 1.3 Ma, reflecting cooling/exhumation of this part of the arc. The mélange south of the arc and the Border Ranges fault, known as the McHugh Complex, comprises sheared metasedimentary rocks, metavolcanic rocks, and chert, and in the Nelchina area it includes a roughly 100-m-diameter block of pillow lavas that are undeformed but altered. Detailed compositional data show that the pillow lava block formed in an intraplate setting. New whole-rock ⁴⁰Ar/³⁹Ar analyses of two pillow-lava samples yielded irregular plateaus with an approximate age of 60 Ma, which we interpret to be largely reset due to reheating. Hypabyssal dikes crosscut the mélange, as well as younger accretionary prism deposits in the area, and provide a new zircon U-Pb age of 53.0 ± 0.9 Ma, which coincides with ages of near-trench plutonism across southern Alaska. This plutonism has been ascribed to subduction of a spreading ridge that migrated eastward along the southern Alaska margin. These new ages constrain the McHugh Complex formation and subsequent hydrothermal alteration to pre-55 Ma. We suggest that the pillow lava was originally part of a Triassic (or earlier) seamount that was decapitated and incorporated into the mélange as the oceanic plate entered the subduction zone. The pillow lava subsequently underwent extensive hydrothermal alteration that almost completely reset its age during the ridge subduction event. We further posit that the Talkeetna volcanic arc and its associated accretionary prism sediments were in their current configuration during the ca. 55 Ma plutonism that was common throughout southern Alaska.
    • Rocket and lidar studies of waves and turbulence in the Arctic middle atmosphere

      Triplett, Colin Charles; Collins, Richard L.; Weingartner, Thomas; Newman, David; Lehmacher, Gerald; Bhatt, Uma S. (2016-08)
      This dissertation presents new studies of waves and turbulence in the Arctic middle atmosphere. The study has a primary focus on wintertime conditions when the largescale circulation of the middle atmosphere is disrupted by the breaking of planetary waves associated with sudden stratospheric warming (SSW) events. We used ongoing Rayleigh lidar measurements of density and temperature to conduct a multi-year study of gravity waves in the upper stratosphere-lower mesosphere (USLM) over Poker Flat Research Range (PFRR) at Chatanika, Alaska. We analyzed the night-to-night gravity wave activity in terms of the wind structure and the ageostrophy. We find that the weak winds during disturbed conditions block the vertical propagation of gravity waves into the mesosphere. The gravity wave activity is correlated with the altitudes where the winds are weakest. During periods of weak winds we find little correlation with ageostrophy. However, during periods of stronger winds we find the USLM gravity wave activity is correlated with the ageostrophy in the upper troposphere indicating that ageostrophy in this region is a source of the gravity waves. Inter-annually we find the wintertime gravity wave activity is correlated with the level of disturbance of the middle atmosphere, being reduced in those winters with a higher level of disturbance and weaker winds. We used rocket-borne ion gauges to measure turbulence in the wintertime middle atmosphere while documenting the larger meteorological context from Rayleigh lidar and satellites. This investigation of turbulence was called the Mesosphere-Lower Thermosphere Turbulence Experiment (MTeX). During MTeX we found a highly disturbed atmosphere associated with an SSW where winds were weak and gravity wave activity was low. We found low levels of turbulence in the upper mesosphere. The turbulence was primarily found in regions of convective instability in the topside of mesospheric inversion layers (MILs). The strongest and most persist turbulence was found in a MIL that is associated with the breaking of a monochromatic gravity wave. These MTeX observations indicate that turbulence is generated by gravity wave breaking as opposed to gravity wave saturation. These MTeX findings of low levels of turbulence are consistent with recent model studies of vertical transport during SSWs and support the view that eddy transport is not a dominant transport mechanism during SSWs.
    • Rogue bulldozers and other essays

      Marsh, Amy; Brightwell, Gerri; Stanley, Sarah; Farmer, Daryl (2016-05)
    • The role and spirituality in Athabascan recovery and sobriety

      Scoville, Dolores Gregory (2003-05)
      It is well documented that Alaska leads the nation in alcohol dependence and abuse. There are studies that document the high abuse levels among Alaska Natives along with corresponding economic costs and lost productivity. The purpose of this study was: (a) to determine the definition of spirituality of a purposive sample of Athabascan Indians of Interior Alaska and (b) to discover what role spirituality plays in Athabascan recovery and sobriety. Nine life history interviews were examined from the People Awakening Project at the University of Alaska Fairbanks. A Grounded Theory Analysis was used to yield culturally relevant results. A definition of spirituality was determined and the role that spirituality plays in Athabascan recovery and sobriety was discovered. Athabascan recovery does not correspond entirely with traditional western treatment methods but there are some similarities in the recovery process common to both. Four of the nine interviews discussed attendance of AA groups or counseling as a help in their recovery. It is recommended that further study with other Alaska Native groups would be beneficial to identify protective and resiliency factors of spirituality and determine how to incorporate these factors for prevention of alcohol dependence.
    • The role of Alaskan missile defense in environmental security

      Fritz, Stacey Anne (2002-12)
      In 2002, the United States abandoned the Anti-Ballistic Missile Treaty and began constructing a missile defense system in Alaska. Questions about how missile defense will contribute to U.S. security remain. Moreover, beliefs about what constitutes security are expanding to include considerations of global environmental stability. According to environmental security theories on arms control, non-proliferation, and environmental degradation, deploying missile defense may make the U.S. and the world less secure. This analysis addresses the issue by exploring the military's role in Alaska and resulting environmental damage, followed by a history of missile defense systems and a description ofthe Alaskan project's components. Arguments for and against missile defense are explained, and the history of Kodiak Island's rocket launch facility illustrates how these issues are evolving in Alaska. The conclusion discusses why pursuing the system is seen by many as a risky policy choice in both traditional and environmental security contexts.
    • Role Of Antennas And The Propagation Channel On The Performance Of An Ultra Wide Band (Uwb) Communication System

      Venkatasubramanian, Arun; Sonwalkar, Vikas (2007)
      The objectives of this dissertation are to experimentally and numerically quantify the effect of antennas and the propagation channel on the performance of an Ultra Wide Band (UWB) receiver. This work has led to the following new results: (1) the variation in the time duration of the impulse response of the oval dipole in the vertical plane is within 5% up to an angle theta = 60° off the broadside direction (theta = 90°); at larger angles a factor of six elongation in the time duration of the impulse response along the antenna axis (theta = 0°) is observed, (2) for an axial ratio of 0.5, the oval dipole has a Voltage Standing Wave Ratio (VSWR) of 2:1 (~11% reflection coefficient) in a 3.1 GHz bandwidth with a lower cut off frequency of 2.8 GHz; for an axial ratio of 2.0 this scales to 0.5 GHz bandwidth with a lower cut off frequency of 1.75 GHz, (3) a new theoretical model has been developed for UWB pulse propagation over the ground which takes into account the geometrical properties of the propagation channel (such as the heights of the transmitter (h1) and the receiver (h2) over the ground) and the nature of the radiated UWB pulse (such as pulse duration (taup) and cycle time (tauc)), (4) an improvement in bit error rate by up to a factor of 100 can be achieved for a matched filter receiver by careful orientation of the transmitting and the receiving oval dipole antennas used in the measurements presented in this dissertation.
    • Role of antioxidant supplementation and exercise regimen in handling oxidative stress from natural PM2.5 exposure due to boreal forest fire

      Witkop, Jacob J.; Dunlap, Kriya; Duffy, Lawrence; Reynolds, Arleigh (2019-05)
      Particulate matter 2.5 (PM2.5) exposure induces oxidative stress that causes many negative health outcomes such as cancer, cardiovascular disease and neurodegenerative disease. Research shows that dietary antioxidants and an up-regulated endogenous antioxidant response from exercise play key roles in the antioxidant defense against oxidative stress. This study is the first to use an animal model to investigate the cumulative effects of using lifestyle interventions of antioxidant supplementation (Arthrospira platensis) and exercise regimen on the antioxidant response before, during, and after ambient PM2.5 exposure. In a two-factorial, longitudinal design, sled dogs (n=48) were divided into four groups (exercise and supplemented, exercise, supplemented, and control) to (1) test the effects of exercise and antioxidant regimen on antioxidant response after one month of implemented exercise and supplementation protocol and (2) measure the antioxidant response of all groups during and after a natural forest fire event in 2015. Commercial assays for Total antioxidant Power (TAP) and the enzymatic antioxidant Superoxide Dismutase (SOD) were used as markers for the total antioxidant response and the endogenous response at all time points. During the forest fire, SOD was increased 5-10-fold over pre/post-exposure levels in all groups suggesting potential implication for using SOD as a marker for the acute response to environmental stress. TAP was increased in the exercise groups after one month of exercise protocol implementation, demonstrating the cytoprotective increase of antioxidants after repeated exercise.
    • Role of Arctic Sea Ice Variability in Climate Models

      Dammann, Dyre O.; Bhatt, Uma; Polyakov, Igor; Zhang, Xiang (2011-08)
      Arctic sea ice plays an important role in climate by influencing surface heat fluxes and albedo, so must be accurately represented in climate models. This study finds that the fully coupled ice-ocean-atmosphere-land Community Climate System Model (CCSM3.0) underestimates day-to-day ice variability compared to observations and employs the Community Atmosphere Model (CAM3.0) to investigate the atmospheric sensitivity to sea ice variability. Three 100-ensemble experiments are forced with climatological, daily-varying, and smoothly-varying sea ice conditions from an anomalously low ice period (September 2006-February 2007). Daily ice variability has a large local impact on the atmosphere when ice undergoes rapid changes, leading to local cooling and subsequent circulation changes. The most notable example of a large-scale atmospheric response occurs over Northern Europe during fall where daily ice variability forces reductions in the number and strength of cyclones, leading to positive sea level pressure anomalies, surface warming, and reduced cloud cover.
    • Role Of Conductivity Spatial Structure In Determining The Locations Of Sprite Initiation

      Tavares, Fernanda De Sao Sabbas; Jeffries, Martin O. (2003)
      Sprites are transient optical signatures of mesospheric electrical breakdown in response to lightning discharges. Multiple sprites are often observed to occur simultaneously, laterally displaced from the underlying causative cloud-to-ground (CG) lightning discharge. The causes of this lateral displacement are presently not understood. This dissertation investigates the role of neutral density perturbations in determining the locations of sprite initiation. The work was performed in three interrelated studies. (1) A detailed statistical study of the temporal-spatial relationships between sprites and the associated CG was performed for July 22, 1996. The distribution of sprite offsets relative to the underlying lightning had a mean of ~40 km. The distribution of sprite onset delays following the parent lightning had a mean of ~20--30 ms, consistent with theoretical estimates for the electron avalanche-to-streamer transition in the mesosphere. (2) A follow-up study for the same observations was performed to investigate the relationship of the sprites to convective activity in the underlying thunderstorm, using GOES-8 infrared imagery of cloud-top temperatures. The sprite generating thunderstorm was a Mesoscale Convective System (MCS). The maximum sprite and -CG production of the system were simultaneously reached at the time of maximum contiguous cloud cover of the coldest region, corresponding to the period of greatest convective activity of the system. Thunderstorm convective activity is a potential source of gravity waves and mesospheric turbulence. (3) Computer simulations of the temporal-spatial evolution of lightning-induced electric fields in a turbulent upper atmosphere were performed. The modeled turbulence in the simulations spanned the amplitude range 10% to 40% of the ambient background neutral density, with characteristic scale sizes of 2 km and 5 km, respectively. The results indicate that neutral density spatial structure, similar to observed turbulence in the mesosphere, facilitates electrical breakdown in isolated regions of density depletions at sprite initiation altitudes. These spatially distributed breakdown regions provide the seed electrons necessary for sprite generation, and may account for the observed sprite offsets.
    • The role of corticosterone and corticosteroid-binding globulin in reproduction of red-legged kittiwakes (Rissa brevirostris)

      Dempsey, Thomas D. (2006-12)
      The goal of this study was to determine to what extent, and by what physiological and behavioral mechanisms, avian reproductive performance is related to environmental variability. Specifically, I explored relationships between components of the physiological stress response, reproductive behavior, and reproductive performance in the red-legged kittiwake (Rissa brevirostris), a long-lived seabird. I found that individuals respond to food-related stress by altering levels of both corticosteroid-binding globulin (CBG) and the primary avian glucocorticoid, corticosterone (Cort). I also found a negative association between breeding adults' Cort concentrations and population-level reproductive success; although no such association existed between CBG and reproductive success. The relationship between Cort and reproductive performance does not appear to result from Cort concentrations affecting an adult's decision to initiate or forego reproduction in a given year. In conclusion, this study suggests that environmentally-induced physiological stress affects reproductive success of red-legged kittiwakes, although the behavioral mechanism remains unknown.
    • Role of dietary fat and supplementation in modulating neurodegenerative pathology in two animal model systems

      Maulik, Malabika; Bult-Ito, Abel; Taylor, Barbara E.; Duffy, Lawrence; Kuhn, Thomas; Dunlap, Kriya (2018-12)
      Neurodegenerative disorders are progressive conditions that worsen over time and results in death of neurons. Parkinson's disease (PD) is a prevalent example of one such age-related disease, which is characterized by movement disorder (ataxia) and/or cognitive disability (dementia). Pathologically, PD is characterized by a toxic accumulation of α-synuclein protein in the midbrain leading to degeneration of the dopaminergic neurons. The etiology of PD is intricate, and the cause is attributed to genetic mutations and environmental factors like insecticides or heavy metals. Moreover, treatment options are limited and often aimed at treating the symptoms rather than the actual disease progression. Using the nematode model of Caenorhabditis elegans, I examined the effect of Alaskan bog blueberry (Vaccinium uliginosum) on α-synuclein overexpression and how such indigenous natural treatment can modulate key molecular targets like sirtuins, which are proteins involved in regulating cellular processes including aging, death and their resistance to stress. The impact of extrinsic factors like dietary fat on PD pathology has been sparsely explored and the molecular basis of such changes is not known. Through my thesis research, I also further investigated the influence of fat metabolism on key hallmarks of PD: α-synuclein overexpression and dopaminergic degeneration in the nematode model. Finally, I studied the interaction of dietary fat (normal, low and high fat) and Alaskan blueberry supplementation on metal induced neurotoxicity model of Mus musculus. Our results highlight the beneficial properties of Alaskan blueberries in combating proteotoxic stress and inflammation in both animal models. They also reiterate the benefit of low fat diet, on its own or in combination with supplementation in improving several PD-like molecular features and how consuming high fat can mask such health promoting outcomes. The current thesis work therefore, provides a foundation for further exploration of neurobiological changes associated with consumption of natural products and different diets and how such alterations can be extrapolated to humans.
    • The role of environmental factors in regional and local scale variability in permafrost thermal regime

      Cable, William Lambert; Romanovsky, Vladimir E.; Christiansen, Hanne H.; Elberling, Bo; Yoshikawa, Kenji (2016-08)
      Global climate change is a topic of great concern and research interest because there are still many components of the Earth System which we do not fully understand and cannot predict how they will respond to this change. One of these components is the permafrost that underlies approximately 24% of the Northern Hemisphere land surface. Permafrost is a thermal condition, found primarily at higher latitudes and elevations, in which subsurface material remains below 0 °C for at least two, but often up to thousands of years. As such, permafrost can accumulate large amounts of carbon in the form of organic material that remains frozen, unavailable for decomposition. However, as the climate warms, permafrost warms and thaws, slowly making this stored carbon available for decomposition into greenhouse gases, which have the potential to create a large positive feedback to climatic warming. A major challenge in permafrost research is that it is not possible to directly obtain spatial information about permafrost through remote sensing alone. This means that we must infer the presence or absence of permafrost and its thermal state based on other remotely sensible parameters such as vegetation, land surface temperature, and topography using a combination of modelling and remote sensing. To do this, we must understand the effects of different environmental factors, such as vegetation, hydrology, topography, and snow on the ground thermal regime and permafrost. In this thesis, the effects of these environmental factors are examined in relation to permafrost presence or absence and the ground thermal regime on a regional and local scale. The regional scale study focuses on the use of vegetation communities, ecotypes, as integrators of variation in environmental factors to influence the ground thermal regime. At the local scale, the microtopography created by ice-wedge polygons is examined as a cause of variations in environmental factors and the impact this has on the permafrost thermal regime of these features. We find that at both scales, remotely sensible parameters such as ecotypes and microtopography show great promise in the efforts to scale-up both field measurements and modelling results.
    • The role of fire in the carbon dynamics of the boreal forest

      Balshi, Michael S. (2007-12)
      The boreal forest contains large reserves of carbon, and across this region wildfire is a common occurrence. To improve the understanding of how wildfire influences the carbon dynamics of this region, methods were developed to incorporate the spatial and temporal effects of fire into the Terrestrial Ecosystem Model (TEM). The historical role of fire on carbon dynamics of the boreal region was evaluated within the context of ecosystem responses to changing atmospheric CO₂ and climate. These results show that the role of historical fire on boreal carbon dynamics resulted in a net carbon sink; however, fire plays a major role in the interannual and decadal scale variation of source/sink relationships. To estimate the effects of future fire on boreal carbon dynamics, spatially and temporally explicit empirical relationships between climate and fire were quantified. Fuel moisture, monthly severity rating, and air temperature explained a significant proportion of observed variability in annual area burned. These relationships were used to estimate annual area burned for future scenarios of climate change and were coupled to TEM to evaluate the role of future fire on the carbon dynamics of the North American boreal region for the 21st Century. Simulations with TEM indicate that boreal North America is a carbon sink in response to CO₂ fertilization, climate variability, and fire, but an increase in fire leads to a decrease in the sink strength. While this study highlights the importance of fire on carbon dynamics in the boreal region, there are uncertainties in the effects of fire in TEM simulations. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. Future studies should incorporate the role of dynamic vegetation to more accurately represent post-fire successional processes, incorporate fire severity parameters that change in time and space, and integrate the role of other disturbances and their interactions with future fire regimes.
    • Role of fire severity in controlling patterns of stand dominance following wildfire in boreal forests

      Shenoy, Aditi; Kielland, Knut; Johnstone, Jill F.; Kasischke, Eric S.; Ruess, Roger W. (2016-05)
      Global trends of climate warming have been particularly pronounced in northern latitudes, and have been linked to an intensification of the fire regime in Arctic and boreal ecosystems. Increases in fire frequency, extent, and severity that have been observed over the past several decades are expected to continue under a warming climate. Severe fires can drastically reduce or remove the deep organic layers that accumulate in mature black spruce forests. Extensive studies in the boreal forests of interior Alaska and Canada have shown that parts of the landscape that undergo severe burning provide favorable seedbeds for the recruitment of deciduous tree seedlings, and thereby reduce the relative abundance of coniferous seedling recruitment in these areas shortly after fire. The persistence of deciduous species such as aspen beyond the seedling recruitment and establishment stage is as yet relatively unknown. To address this knowledge gap, I asked the question: is increased deciduous recruitment observed in severely burned areas transient, or does it result in persistent changes in stand composition later in succession? I examined changes in relative dominance patterns of aspen and black spruce that had occurred between 8 and 14 years post-fire along an organic layer depth gradient within a single burn. I found that patterns of relative species dominance established shortly after fire persisted into the second decade of succession, resulting in productive aspendominated stands in severely burned areas with shallow organic layers, and black spruce dominated stands in lightly burned areas with deep organic layers. These patterns of stand dominance in relation to post-fire organic layer depth were also observed in several other burns in the region. Therefore, deep burning fires are likely to result in a persistent shift from black spruce to aspen dominance in severely burned parts of the boreal forest. In order to understand how variation in organic layer depth is driving these alternate successional pathways, I measured nutrient uptake rates of aspen and spruce in severely and lightly burned sites within a single burn. I also examined relationships between post-fire organic layer depth and a suite of soil variables, and evaluated the relative importance of these soil variables in explaining variation in stand level aspen biomass, spruce biomass, and the relative dominance of aspen vs. spruce. I found that variations in post-fire organic layer depth result in contrasting soil environments, with soils in shallow organic layer sites being warmer, drier, and more alkaline than soils in deep organic layer sites. Variations in aspen biomass and aspen: spruce biomass were largely being driven by substrate conditions, whereas stand level spruce biomass was less sensitive to these same variations in soil conditions. Nutrient uptake rates of both aspen and spruce were higher in severely burned areas with shallow organic layers, but the differences between species were magnified by stand biomass patterns in relation to post-fire organic layer depth. My results suggest that the positive effects of soil conditions associated with mineral soil substrates extend well beyond the initial seedling recruitment phase, and may continue to influence aspen growth rates into the second decade of succession resulting in the differential patterns of biomass accumulation and stand dominance in relation to post-fire organic layer depth. With the predicted increase in fire severity and shortening of the fire cycle, the proportion of aspen dominated stands on the landscape is likely to increase, which will incur substantial changes in ecosystem function (e.g., land-atmosphere energy exchange, C and N storage, nutrient cycling, net primary productivity, and wildlife habitat quality) compared to the current forests dominated by conifers.
    • The role of glycerol-3-phosphate acyltransferase 1 in mitochondrial phospholipid biosynthesis of cold-bodied fishes

      Keenan, Kelly Anne; O'Brien, Kristin; Schulte, Marvin; López, Andrés; Harris, Michael (2015-08)
      Mitochondrial biogenesis is induced by low temperature in many fish species. For example, cold acclimation of Gasterosteus aculeatus (threespine stickleback) increases mitochondrial densities in oxidative skeletal muscle. Oxidative muscles of Antarctic icefishes (suborder Notothenioidei) also have high mitochondrial densities characterized by higher densities of phospholipids compared to red-blooded notothenioids. Mitochondrial biogenesis has been well studied in mammals yet it is unknown how mitochondrial phospholipid synthesis is regulated. I hypothesized that both activity and mRNA levels of glycerol-3-phosphate acyltransferase (GPAT), the rate-limiting enzyme in glycerolipid biosynthesis, would increase in oxidative muscle of stickleback, where mitochondrial biogenesis occurs, but not in liver, in response to cold acclimation, and that GPAT1 and /or GPAT2 mRNA levels would be higher in hearts of icefishes compared to red-blooded species. To test these hypotheses, maximal activity of GPAT and mRNA levels of GPAT1 and GPAT2 were measured in liver and oxidative muscle of coldand warm- acclimated stickleback. GPAT1 and GPAT2 mRNA levels were also quantified in hearts and livers of red- and white-blooded Antarctic notothenioids. Additionally, cDNA of GPAT1 was sequenced in Antarctic and sub-Antarctic notothenioids to gain insight to the evolution of a mitochondrial membrane protein and identify candidate amino acid residues responsible for maintaining function at cold temperature. GPAT activity increased in oxidative muscle but not in liver, and transcript levels of GPAT1 increased in liver but not in oxidative muscle, in response to cold acclimation in stickleback. GPAT2 transcripts were undetectable in both tissues. GPAT1 mRNA levels were highest in liver of red-blooded Antarctic notothenioids and did not differ in hearts between red- and white-blooded fishes, and GPAT2 transcripts were undetectable. GPAT protein levels may not change concurrently with GPAT1 and GPAT 2 mRNA levels because GPAT3 or 1-acylglycerol-3-phosphate acyltransferase (AGPAT), the enzyme subsequent to GPAT, may be involved in regulating phospholipid synthesis during mitochondrial biogenesis. The amino acid sequence of GPAT1 is highly conserved (97.94-98.06%) among Antarctic and sub-Antarctic notothenioids, with three potential sites in the cytosolic region that may be important for maintaining function at cold temperature: Ser415Ala, Asp603Glu and Thr648Ala.
    • Role of ionospheric conductance in magnetosphere-ionosphere coupling

      Bhattacharya, Tapas; Otto, Antonius; Bristow, William; Conde, Mark; Lummerzheim, Dirk; Ng, Chung-Sang (2014-08)
      Magnetosphere-ionosphere (MI) coupling has been studied for a long time. However, not much work has been done on a systematic understanding of the relation between ionospheric Pedersen conductance, its effect on the evolution and modification of field-aligned currents (FACs), and the influence of conductance and FACs on the formation of parallel electric fields which cause particle precipitation. Though the roles of ionospheric conductance gradients for FACs and parallel electric field evolution are directly related, they are poorly understood. This dissertation advances the understanding of these areas and all results of this study are based on numerical simulations that employ a three-dimensional - two-fluid (ions and neutrals) simulation code. The first part of this dissertation presents a systematic study of the magnetospheric and ionospheric influences on the evolution and modification of FACs with focus on the role of ionospheric Pedersen conductance and its gradients. FACs are typically generated in the magnetosphere and are carried into the ionosphere by Alfvén waves. During their reflection from the ionosphere these FACs are modified depending on the magnitude and distribution of ionospheric conductance. For conductance gradients along the polarization of the wave, strong Pedersen currents can be generated which in turn enhance the FAC as well. The second part of this dissertation addresses the properties and evolution of parallel electric fields in an attempt to better understand the formation of discrete auroral arcs in response to the evolution of FACs for predetermined ionospheric conductance patterns. Frequently, auroral acceleration is believed to occur through U or V shaped potentials. Therefore, this part examines the properties of localized parallel electric fields in a uniform magnetic field. It is demonstrated that localized parallel electric fields generate magnetic flux in the absence of source of free energy. It is also shown that parallel electric fields generated in a FAC in the presence of a (anomalous) resistivity represent a load and can provide physical explanation for the auroral acceleration geometry. The results demonstrate that such electric fields can be significantly enhanced by Alfvén wave reflection where both magnitude and gradients of the ionospheric conductance are important. The strongly enhanced parallel electric field is associated with magnetic reconnection and modifies the FAC system such that thin current layers (with curls and folds) are observed to be embedded in the large scale current system.
    • The role of mammalian herbivores in primary succession on the Tanana River floodplain, interior Alaska

      Butler, Lemuel Gordon (2003-12)
      I compared willow (Salix) communities along the Tanana River exposed to varying levels of herbivory to examine how herbivory influences the landscape distribution of vegetation. Moose (Alces alces) and snowshoe hare (Lepus americanus) herbivory decreased plant biomass and canopy height and increased the proportion of dead stems in willow communities. Herbivory also shifted the age distribution of plants in willow communities towards younger age classes, and also decreased the number of communities dominated by willow on the landscape. A frame-based simulation model was built to incorporate the effects of herbivory and river fluvial dynamics on plant succession. My results show that herbivory, erosion and accretion are all necessary components to accurately model the landscape distribution of vegetation communities. Erosion/accretion had a major role in landscape vegetation patterns shifting the landscape toward earlier successional communities, while herbivory had a minor role, shifting the landscape towards later successional communities. The interactions among these biotic and abiotic processes account for the empirically observed landscape vegetation patterns.