• Numerical simulation of thermo-mechanical behavior of gypsum board wall assembly

      Quan, Zhili; Hulsey, J. Leroy; Ahn, Il Sang; Chen, Cheng-fu; Xiang, Yujiang (2019-05)
      Fire safety has become a significant concern to public safety; especially in the aftermath of 9/11 attack where, according to official reports, three World Trade Center buildings collapsed because of fire. Therefore, the level of thermal insulation required from building material and structural elements has increased. In recent years, gypsum board wall assemblies have been increasingly used as compartmentation for high-rise residential and commercial buildings. The increasing popularity of gypsum board wall assemblies is due to their relatively high strength-to-weight ratio, ease of prefabrication, fast erection and good thermal insulation. Before implementation of any building material or structural element, its Fire Resistance Rating must be determined by subjecting the material or element to a standard furnace fire test. Over the years, a large database has been collected for the Fire Resistance Rating of building materials and structural elements. However, due to the expensive and time-consuming nature of the standard fire tests, determining an accurate Fire Resistance Rating can be a difficult task. In this study, the author numerically evaluated the Fire Resistance Rating of a new gypsum board wall assembly. Composite steel-EPS (Expanded Polystyrene) insulation is added to a traditional gypsum board wall assembly. The author first did numerical simulation of an experiment on the thermal response of a non-load-bearing gypsum board wall assembly to verify the thermal modeling methodology. The author then did numerical simulation of an experiment on the mechanical response of a load-bearing gypsum board wall assembly to verify the mechanical modeling methodology. Finally, the author used the verified thermal and structural modeling methodology to simulate the new composite steel-EPS gypsum board wall assembly and obtained its numerical Fire Resistance Rating. This Fire Resistance Rating should be compared with future experimental results of the new wall assembly. All modeling was done with ABAQUS V6.14.
    • Numerical simulation study to evaluate recovery performance of miscible displacement and WAG process

      Wu, Xingru (2002-08)
      Several factors including gravity segregation, solvent types, injection methods, and production/injection well constraints are known to impact the performance of Water-Alternate-Gas (WAG) process and miscible displacement. This thesis studies well completions to optimize the miscible displacement and WAG processes through numerical simulation of a pattern model with stochastic permeability distribution. To study the impact of well placement and completions on miscible performance in heterogeneous media, we injected various solvents and examined the effect of gravity segregation, permeability distribution and anisotropy, horizontal well lengths, orientation of vertical and horizontal wells on oil recovery. Also, we conducted simulations with various WAG ratios and cycle lengths to understand the WAG processes. Performance of miscible gas flooding and WAG process are compared to that of waterflooding.
    • Numerical Studies Of Tectonic And Landslide-Generated Tsunamis Caused By The 1964 Great Alaska Earthquake

      Suleimani, Elena; Hansen, Roger (2011)
      The focus of my thesis is on the complex source mechanism of tsunami waves generated by the MW9.2 1964 Alaska earthquake, the largest instrumentally recorded earthquake in North America. The vertical seafloor displacements produced a trans-Pacific tectonic tsunami that caused loss of life and great damage in Alaska and the west coast of the United States and Canada. In addition to the major tectonic wave, about 20 local tsunamis were generated by submarine mass failures in a number of bays and fjords in south-central Alaska. These locally generated waves caused most of the damage and accounted for 76% of tsunami fatalities. I use numerical modeling to study tectonic and landslide tsunamis of the 1964 earthquake. The first part of the thesis presents numerical analysis of tsunami inundation at Seward and other locations in Resurrection Bay caused by the combined impact of landslide-generated waves and the tectonic tsunami. This study utilizes the recent geological findings of large-scale submarine slope failures in the bay during the 1964 earthquake and confirms the hypothesis that tsunami waves observed in Seward during and immediately after the earthquake resulted from multiple underwater landslides. The analysis of the simulated composite inundation area caused by the two different tsunami sources explains their relative contributions and demonstrates good agreement with observations. The second major topic is the source of the 1964 tectonic tsunami. The results of inundation modeling in Kodiak Island show that tsunami runup in the near field strongly depends on coseismic slip in the Kodiak asperity. I test the hypothesis that splay faults played a major role in tsunami generation and evaluate the extent of the Patton Bay fault using near-field tsunami observations. The new source function of the 1964 tsunami is presented, which includes the effects of the splay fault displacements and the component of the vertical deformation of the sea surface due to horizontal displacements on the megathrust. The results of numerical modeling studies included in this thesis complement the Alaska Tsunami Inundation Mapping Project. This activity provides emergency officials in coastal Alaska with tsunami hazard assessment tools and helps mitigate future tsunami risk.
    • Numerical study of an exhaust heat recovery system using corrugated tubes and twisted tape inserts

      Mokkapati, Vamsi Krishna Sarma; Peterson, Rorik; Das, Debendra; Kim, Sun Woo; Lin, Chuen-Sen (2014-12)
      Diesel engine generators are the major power source for small communities in cold regions. Diesel generators waste about 1/3 of their fuel energy in the form of heat through exhaust gas. The primary goal of this work is to capture part of the heat from the exhaust and improve the efficiency of the system. A gas to liquid heat transfer performance of a concentric tube heat exchanger with corrugated tubes and twisted tape inserts is investigated by considering its effects on engine performance and economics. This type of heat exchanger is expected to be inexpensive to install and effective in heat transfer, with minimal effect on exhaust emissions of diesel engines. Most previous research has investigated liquid to liquid heat transfer in corrugated tubes at low Reynolds, not gas to liquid heat transfer. The SolidWorks Flow Simulation computer program was used to perform these studies. The program is first validated by comparing simulation results with renowned correlations and field measurements. Simulations are then conducted for a concentric tube heat exchanger with corrugated tubes and twisted tapes of different configurations to determine the optimal design. The maximum enhancement in the rate of heat transfer was found in an annularly corrugated tube heat exchanger with twisted tape inserts. This exchanger transfers about 235.3% and 67.26 % more heat compared to plain tube and annularly corrugated tube heat exchangers without twisted tapes, respectively. Based on optimal results, for a 120 kWe diesel generator, the application of an annularly corrugated tube heat exchanger with twisted tape inserts can save 2,250 gallons of fuel annually (a cost of approximately $11,330) expected payback of initial cost in one month. In addition, saving heating fuel also reduces CO₂ emissions by 23 metric tons per year.
    • Numerical Study Of The Atmospheric Radiative Transfer Process With Application To The Arctic Energy Balance

      Tsay, Si-Chee; Stamnes, Knut H.; Jayaweera, Kolf; Fritts, David C.; Lee, Lou-Chuang; Piacenza, Robert J.; Shaw, Glenn E. (1986)
      A high-order discrete-ordinate approximation is utilized to solve the radiative transfer equation for both solar and terrestrial spectra. The solutions have been compared with other methods and found to be reliable and efficient. These solutions have been used to construct a complete and comprehensive radiation model for the arctic atmosphere. The bulk radiative properties (e.g. fluxes and heating/cooling rates) as well as the angular distribution of intensity can be computed as functions of wavelength at various levels in vertically inhomogeneous atmospheres. The radiation model treats Rayleigh scattering, gaseous absorption/emission, scattering and absorption/emission by cloud droplets and haze particles. Snow conditions of the arctic region are simulated by snow grains and soot contamination in the surface layers. A unified treatment of shortwave and longwave radiative transfer is achieved. Use has been made of the five McClatchey atmospheres and of data from the Arctic Stratus Clouds Experiment collected in 1980. Results are compared among broad-band, narrow-band and line-by-line (restricted to gases) computations. We find that at the expense of accuracy by a few watts.m('-2) for flux or a few tenth (DEGREES)C/day for heating/cooling rate computations, the broad-band models are very fast and suitable for certain types of climate modelling. During the arctic summer, stratus clouds are a persistent feature and decrease largely the downward flux at the surface. Arctic haze is important if it is above the cloud layer or in air with low relative humidity and also decreases the downward flux at the surface. The greenhouse effect of doubling the CO(,2) amount can be offset by the haze condition or by the increase in cloudiness of about 4%. In late June, we find that a clear sky condition results in more available downward flux for snow melt than does a cloudy sky condition. This is because the increase of infrared radiation diffused back to surface by the cloud can not compensate the reduction of solar radiation. If the snow starts to melt, the decreasing snow albedo further accelerates the melting process.
    • Numerical tidal models with unequal grid-spacing

      Mungall, J. C. H. (1973-05)
      A two-dimensional alternating-direction implicit numerical tidal model with unequal grid-spacing is developed and successfully tested. The method is essentially an extension into two dimensions of a one-dimensional implicit method in which tide heights and flow rates are evaluated on the same cross-sections, an approach which permits a river to be schematized into a number of sections of differing lengths. The two-dimensional scheme gives the user considerable control over the density of the computation points in a region by virtue of the fact that heights and depth-mean currents are evaluated midway between points of intersection of a grid constructed from orthogonal lines, the spacing between which may be chosed at will. The method is applied initially to the Irish Sea using a grid of constant spacing. The effects of increasing time step and friction on stability and accuracy are investigated, and the model is proved to be unconditionally stable. The results match those of previous investigators, and some new information on the M₂ currents of the region is obtained. The second application of the model is to a 'rectangular' North Sea, a favorable comparison being obtained when the region is schematized by two grids of equal and unequal spacing. Finally, the model is applied to Cook Inlet, Alaska, a region of complexity sufficient to warrant the use of a scheme possessing the unequal grid-spacing feature. Satisfactory results are obtained after tuning the model by adjustment of the friction coefficient. Movie films were made in order to conceptually clarify the tidal behaviors of the Irish Sea and Cook Inlet. Each film shows as functions of time, perspective views of the sea surface, and current vectors superimposed on a contour map of the sea surface.
    • Nuniwarmiut Land Use, Settlement History And Socio-Territorial Organization, 1880--1960

      Pratt, Kenneth L. (2009)
      Prior efforts to identify traditional socio-territorial groups among the Central Yup'ik Eskimos of southwestern Alaska have been primarily theoretical in nature, examined the subject from very restricted temporal perspectives, and were heavily reliant on a small body of written historical accounts---none of which were informed by contacts with indigenous populations across the entire region. The collective results are inconsistent and largely unverifiable; hence many basic details about Yup'ik socio-territorial organization remain obscure. This study deviates from its predecessors in geographical focus, temporal scope and methodology. The geographical focus is on the Nuniwarmiut (or Nunivak Eskimos), both the most isolated and best documented of all Central Yup'ik populations. Its temporal scope covers a period of 80 years, the earliest point of which marks the practical limits of reliability of the available ethnographic data. Finally, the study's methodology is ethnohistorical; it employs a rich array of complementary historical, ethnographic and archeological data to produce a far more detailed account of socio-territorial organization than has been compiled for any other population in the region. The findings indicate socio-territorial organization among the Nuniwarmiut took the form of local groups organized around winter villages. The functional stability of each group was susceptible to various natural and cultural factors; in fact, such groups ranged in number from as many as 30 to as few as 7 over the course of the study period. The Nuniwarmiut society was a level of identity above the local group; it was comprised of the totality of local groups that existed at any point in time, but was not itself a socio-territorial unit. Overall, the study demonstrates that socio-territorial organization among the Nuniwarmiut was substantially more complex and dynamic than previously recognized.
    • Nutrient And Contaminant Dynamics In The Marine Food Web Of Kotzebue Sound (Alaska)

      Moses, Sara K.; O'Hara, Todd (2010)
      The objectives of these studies were to document nutrient and contaminant concentrations in upper trophic level organisms of the Kotzeue, Alaska marine food web; address associated risks and benefits to human consumers of these species; understand the drivers of nutrient and contaminant patterns and concentrations; and test the limitations of chemical feeding ecology tools used to trace nutrient and contaminant pathways within this food web. Tissues of subsistence harvested animals were analyzed for nutrients, contaminants and stable isotopes (delta13C and delta15N). Foods derived from sheefish (Stenodus leucicthys) and spotted seal (Phoca largha) provide numerous essential nutrients, with limited risk from contaminant exposure. Food processing altered nutrient and contaminant concentrations and stable isotope ratios, warranting the evaluation of foods as they are ultimately consumed when determining the risks and benefits of traditional diets. delta13C and delta15N, common chemical tracers of feeding ecology and contaminant pathways in food webs, varied widely by tissue type. delta15N and mercury did not differ consistently among seal tissues. Consequently, when utilizing stable isotopes as tracers of feeding ecology and mercury exposure, the specific tissue consumed and the processed state of the tissue should be considered. Bioaccumulation patterns differed between sheefish and spotted seals in relation to their respiratory physiology and persistent organic pollutant (POP) partitioning behavior between lipids and the respiratory medium (i.e., air versus water). Certain POPs that do not bioaccumulate in fish due to rapid excretion across the gills into surrounding waters (low KOW) do bioaccumulate in seals if not efficiently eliminated via the lungs to the air (high K OA). Thus, KOW alone cannot predict bioaccumulation in mammals. Regulatory guidelines must incorporate KOA into chemical risk-assessments for air-breathing species, including humans and marine mammals. Ringed ( Phoca hispida), spotted and bearded (Erignathus barbatus ) seals had distinct blubber fatty acid (FA) signatures. Blubber of ringed and spotted seals exhibited significant stratification relative to both FA degree of unsaturation and carbon chain length. FA stratification appears largely driven by the steep temperature gradient of blubber, except in the case of polyunsaturated FA (PUFA) which may be maintained in the inner blubber for rapid mobilization to meet physiological requirements.
    • Nutrient Dynamics In The Northern Gulf Of Alaska And Prince William Sound: 1998--2001

      Childers, Amy Ruehs; Whitledge, Terry (2005)
      The northern Gulf of Alaska (GOA) shelf is a productive coastal region that supports several commercially important fisheries. The mechanisms supporting such high levels of productivity over this shelf are not understood, however, since it is a downwelling-dominated shelf. In an effort to understand the mechanisms underlying such high biological productivity, nutrient distributions were determined 25 times throughout 1998, 1999, 2000, and 2001 from over the northern GOA shelf and in Prince William Sound (PWS). Deep water (>75 m) nitrate, silicate and phosphate concentrations were positively correlated with salinity indicating an offshore nutrient source. The average annual cycle was established, in which nitrate, silicate and phosphate responded seasonally to physical and biological processes. Ammonium concentrations were generally low and uniform (<1.2 muM) with occasional patches of higher concentrations. During each summer, an onshore flux of dense nutrient-rich bottom water onto the shelf was evident when the downwelling relaxed. This seasonal flux created nutrient reservoirs over the deeper shelf regions that were eventually mixed throughout the water column during the winter months. This annual evolution may be vital to the productivity of this shelf. A large degree of interannual variability was found during the study, which included El Nino (1998) and La Nina (1999) years. Spring phytoplankton biomass over the shelf was highest in 2000 when the upper waters were nutrient enriched and strongly stratified. The highest phytoplankton biomass was measured in May 1999 during the passage of a slope eddy, which demonstrated the potential of these phenomena to greatly enhance primary productivity. A large degree of spatial variability was also found, both cross-shelf and along-shelf. Hinchinbrook Canyon was found to consistently have high salinity, nutrient-enriched bottom waters suggesting it plays an important role in the transport of slope waters onto the shelf and probably into PWS. Along-shelf trends were found in the upper coastal waters in the winter and spring, with higher salinities, temperatures, and nutrient concentrations upstream of PWS. The nutrient dynamics were similar in PWS and over the shelf/slope in 2001; however, nutrient drawdown, followed by depletion, and the spring bloom appeared earlier and stronger in PWS.
    • Nutritional and behavioral aspects of reproduction in walruses

      Gehnrich, Pauline Hayton (1984-09)
      Walruses (Odobenus rosmarus) at Marineland, California consumed food in increasing amounts as they grew larger out ate less per unit of body weight. Adult males consumed the most food in November - December, then fasted throughout the breeding season. Females apparently fasted during ovulation and birth. Females consumed 50% more energy while pregnant or lactating than when not pregnant or lactating. Male walruses spent more time displaying, and their displays were more stereotyped, during the breeding season. Females initiated and terminated interactions with the males during the breeding season, and those interactions were preceeded by displays. Females vocalized to the calf to initiate suckling bouts, reassure the calf, and to call the calf. Calves vocalized to initiate suckling bouts and indicate danger. When the calf was threatened, the female responded quickly by tusk strikes, kinesic tusk threats, vocal threats, or calling the calf. The calf tended to follow the female.
    • Nutritional and ecological determinants of growth and reproduction in Caribou

      Gerhart, Karen Lynn (1995)
      I investigated the mechanisms by which differences in body weight and body composition (fat, protein) of female caribou (Rangifer tarandus granti) from the Central Arctic and Porcupine herds might determine changes in pregnancy rate and calf growth. Allometric relations between chemical components and body weight variables were highly significant, despite tremendous seasonal changes in composition. Between October 1989 and May 1990, body fat and body protein of adult females of the Central Arctic Herd declined by maxima of 45 and 29%, respectively; an additional 32% of fat was lost by July. Extensive mobilization of fat and protein indicates winter undernutrition. Marked hypertrophy of liver and kidneys in summer suggests the presence of mobilizable protein reserves. Birth weights of calves were similar between sexes, but male calves grew relatively faster during summer and were significantly heavier than females in autumn. Both fat content and growth rate of calves declined between 4 and 6 weeks post-calving, perhaps in response to insect harassment. Weight gains of wild calves were greatly reduced or absent after 100 d of age, while captive calves continued to grow until 175 d, suggesting that first-summer growth of caribou is determined in part by nutrient availability. Birth weight and growth rate of wild calves from birth to 3-4 weeks of age accounted for nearly 79% of the variability in autumn weights, again implying summer nutrient limitation. Female caribou were unable to entirely compensate for the metabolic and ecological costs of lactation: in autumn, lactating females had 42% less fat and 9% less protein than nonlactating females. Unlike females from the Central Arctic Herd, those from the Porcupine Herd did not demonstrate compensatory weight gains over summer; instead, autumn weight was highly correlated to June weight. Probability of pregnancy was positively correlated with body weight and fat content in early winter. Females that extended lactation into November were less fertile than predicted by body size or condition. I believe that these females were exhibiting lactational infertility.
    • Nutritional ecology of moose in an urban landscape

      Welch, Joseph H.; Barboza, Perry; Hundertmark, Kris; Spalinger, Don; Farley, Sean (2012-08)
      Joint Base Elmendorf-Richardson (JBER), Alaska supports a large population of moose that lives in and around the urban and industrial development of Anchorage. This study evaluates the body condition of adult female moose on JBER and calculates the relative nutritional value of habitat for planning development and for mitigating the effects of development on this population. Body condition of moose on JBER was similar to that of other populations of moose in Alaska. Our nutritional model predicted that shrublands could support 11-81 times more moose than any other habitat on JBER. Activity patterns of JBER moose were similar to those published for non-urban moose, indicating habituation to human activity. Activity levels increased as moose moved through higher quality habitats. Sustained production of this heavily utilized population requires maintaining shrublands in undeveloped portions of the base where moose-vehicle collisions can be minimized.
    • Nutritional quality of large round bale silage as affected by compaction, color of wrap, or preservative in Southcentral Alaska

      Lussier, Charlotte L. (2007-05)
      Large round bale silage (LRBS), fermented hay, baled at 45-65% moisture content might be a better product than air-dried hay for farmers and ranchers in Southcentral Alaska. Variable weather and sometimes unfavorable conditions for drying hay to the required 18% moisture content makes high quality hay production unpredictable. Our study was designed to determine what practices might produce the highest nutritional quality LRBS. Treatments included using black and white plastic bale wrap, two different baler compaction levels, and application of a buffered propionic acid preservative. The study used four different forage fields over a two year period. Three fields were harvested on each cutting date. We measured dry matter (DM), neutral detergent fiber, acid detergent fiber, lignin, acid detergent insoluble nitrogen, crude protein, and digestible energy. Fermentation analysis measured levels of lactic, acetic, propionic and butyric acids, ammonia and pH on LRBS. The denser bales, bales wrapped in black plastic, and those treated with preservative produced highest quality forage. Dense bales had lower DM, lower pH, and also had the highest lactic acid. Ammonia levels declined when moisture content decreased.
    • Obfuscation fingerprinting in Android binaries

      Van Veldhuizen, Matthew Philip (2015-04)
      There are many way to protect code from reverse engineering. One such way is to obfuscate either the source code, machine code or bytecode. Obfuscating Android applications not only makes it harder to reverse engineer, it can also speed up execution by reducing the size of the application and removing unnecessary code. One method of obfuscation is to do it manually and the other method is to use an obfuscation program. However, it may become necessary to reverse obfuscation, because of the loss of source code or when investigating malware, trojans, or other harmful applications. This process is called deobfuscation. Once an application has been obfuscated performing deobfuscation is a tedious task, and knowing how the application was obfuscated would increase the probability of correctly reversing the obfuscation. By examining four Android application obfuscators I successfully identified distinct fingerprints within each of the obfuscated binaries by building a simple Android application, obfuscating it, and then comparing obfuscated and unobfuscated bytecode. Using these fingerprints I was able to associate each obfuscator with an approximate probability that it was used to perform the obfuscation.
    • Oblique impact cratering: A comparison of low-velocity experiments to high-velocity experiments

      Hessen, Katie K.; Hessen, Robert; Dean, Ken; West, Michael; Chappelow, John; Christensen, Douglas (2008-12)
      Previous impact cratering experiments performed by Gault and Wedekind (1978), used high-velocity impactors (~1 km/s to 7 km/s) to quantify how impact angle affects crater morphology and ejecta pattern. Low velocity (144 m/s to 260 m/s) impact experiments were conducted in a vacuum chamber with a basaltic sand target material and impact angles ranging from 0.5° to 90° (vertical) at the Impact Cratering Laboratory at the University of Tokyo Kashiwa. The crater morphology and ejecta distribution from low velocity impacts are then compared to results from the higher velocity projectiles. When adjustments are made to the low-velocity measurements to account for differences in velocity, the displaced mass ratio follows a sinθ distribution, as is seen in the high- velocity experiments. In the low-velocity experiments, asymmetric ejecta is present at slightly higher impact angles. The presence of an uprange forbidden zone occurs at the same impact angle (20°) in both sets of experiments. The most striking difference between the two sets of experiments is the complete lack of a downrange forbidden zone in all of the low-velocity experiments. With the exception of the very lowest impact angles, these low-velocity oblique impact experiments yield similar changes in crater characteristics with varying impact angles to the previous high-velocity experiments.
    • Observable effects of attention, posture, ergonomics and movement in the classroom

      Healy, Joanne; Bult-Ito, Abel; Anahita, Sine; Charles, Walkie; Irish, Joel; Kaden, Ute (2014-05)
      Two studies related to student attention, posture, school ergonomics, student behavior (leaning, standing up, and moving), and learning engagement were conducted in Alaska. The Children's Postural Improvement Study (CPIS) looked at the observable effects of two interventions on attention. In the Classroom Environmental Study (CES) a baseline ergonomic survey compared observed student behavior and classroom arrangements. The purpose of the CPIS was to investigate the effects of a postural education program, consisting of five 30-minute instructional sessions, as compared to a nutritional intervention at two elementary schools and its effect on attention. Three quantitative tools measured attention, the post-Partial Vanderbilt ADHD Teacher and Parent rating scales and pre- and post-math fluency tests. Qualitative measures included pre- and postintervention photographs, daily comments from students after the lesson, and post open-ended-question student and teacher surveys. Based on the post-surveys, participants valued their good posture and made concentrated efforts to improve it. Quantitative results of this postural study revealed no correlation between posture and attention. The follow-up CES examined the current state of furniture in 78 classrooms and pedagogical practices in regard to student movement and learning engagement in eight fourth-grade classrooms in three elementary schools. Two-way ANOVA revealed a significant school effect for leaning and significant classroom nested within school effects for leaning, standing up, and moving. Classroom sketches were coded to examine movement and posture. No significant difference for desk clusters by grade, or by school using the Chi-squared test were found, but there was a significant difference comparing the seating relationship to instructional delivery by grade and by school. Recommendations for future research and changes within Schools of Education and school districts to improve posture and learning engagement include: adjust current students' chairs and desks to meet their ergonomic needs; raise awareness of and inform pre-service, current teachers, students, and parents about ergonomic health concepts; encourage teachers to move around the classroom while instructing to engage students as they track the teacher's movement; and limit instructional periods to 20 minutes or less to allow for student movement breaks.
    • Observation and analysis of whistler mode echoes received by RPI on IMAGE at high latitudes

      Chen, Xiangdong (2001-05)
      Whistler-mode wave-injection experiments with Radio Plasma Imager (RPI) on IMAGE offer an opportunity to observe the whistler-mode echoes. We have performed raytracing studies to investigate accessibility of whistler-mode waves injected from IMAGE to various regions of the magnetosphere and also to other satellites such as Akebono. RPI detected both discrete and diffuse whistler-mode echoes during our observing period (April 21 to August 28, 2000) when IMAGE was at a low altitude (1̃000-7000 km) and mid-to-high latitudes (>25 - 40S̊) near its perigee. We believe that the discrete echoes are the result of RPI signals reflected at the Earth-ionosphere boundary and the diffuse echoes are the result of scattering of RPI signals by meter-scale irregularities. Raytracing analysis shows that both ducted and nonducted ray propagation are needed to explain the observed whistler-mode dispersion. Comparison of electron densities obtained from our raytracing analysis of dispersion with the electron densities obtained by Kletzing et al. in the Auroral Zone shows that these density values deduced from RPI data were about ten times higher. This may be because the antenna radiation efficiency is higher at higher electron densities.
    • Observation and analysis on the characteristics of strain induced by frost heave for a full-scale buried, chilled gas pipeline

      Yang, Kun; Huang, Scott; Chen, Gang; Darrow, Margaret (2013-12)
      This thesis examines the strain characteristics of a large-scale, buried chilled gas pipeline in the discontinuous permafrost region. A full-scale chilled pipeline gas experiment was conducted in Fairbanks, Alaska. The test pipeline had a length of 105 m and a diameter of 0.9 m. One-third of the pipeline was located in permafrost and the rest was in non-permafrost. The monitoring data were collected from December 1999 to January 2005 including both freezing and thawing phases. In the transition zone between frozen and unfrozen soil, the foundation experienced a vertical movement caused by differential frost heave. The test results indicated that the bending action was the main factor for the pipeline for the circumferential and longitudinal strain distribution of the pipeline. Moreover, linear relationships were developed between frost heave and the longitudinal strain at the top and the bottom (i.e., 0� and 180�) of the pipe. The developed equations can be used to predict the strain of the pipe caused by differential frost heave for future tests with similar site conditions.