• Predictive Modeling of Avian Influenza in Wild Birds

      Herrick, Keiko; Huettmann, Falk; Taylor, Barbara; Runstadler, Jonathan; Ickert-Bond, Stephanie; Bortz, Eric (Veterinary Research, 2013-05)
      Over the past 20 years, highly pathogenic avian influenza (HPAI), specifically Eurasian H5N1 subtypes, caused economic losses to the poultry industry and sparked fears of a human influenza pandemic. Avian influenza virus (AIV) is widespread in wild bird populations in the low-pathogenicity form (LPAI), and wild birds are thought to be the reservoir for AIV. To date, however, nearly all predictive models of AIV focus on domestic poultry and HPAI H5N1 at a small country or regional scale. Clearly, there is a need and an opportunity to explore AIV in wild birds using data-mining and machinelearning techniques. I developed predictive models using the Random Forests algorithm to describe the ecological niche of avian influenza in wild birds. In “Chapter 2 - Predictive risk modeling of avian influenza around the Pacific Rim”, I demonstrated that it was possible to separate an AIV-positivity signal from general surveillance effort. Cold winters, high temperature seasonality, and a long distance from coast were important predictors. In “Chapter 3 - A global model of avian influenza prediction in wild birds: the importance of northern regions”, northern regions remained areas of high predicted occurrence even when using a global dataset of AIV. In surveillance data, the percentage of AIV-positive samples is typically very low, which can hamper machine-learning. For “Chapter 4 - Modeling avian influenza with Random Forests: under-sampling and model selection for unbalanced prevalence in surveillance data” I wrote custom code in R statistical programming language to evaluate a balancing algorithm, a model selection algorithm, and an under-sampling method for their effects on model accuracy. Repeated random iv sub-sampling was found to be the most reliable way to improved unbalanced datasets. In these models cold regions consistently bore the highest relative predicted occurrence scores for AIV-positivity and describe a niche for LPAI that is distinct from the niche for HPAI in domestic poultry. These studies represent a novel, initial attempt at constructing models for LPAI in wild birds and demonstrated high predictive power.
    • Predictive Performance Of Machine Learning Algorithms For Ore Reserve Estimation In Sparse And Imprecise Data

      Dutta, Sridhar; Bandopadhyay, Sukumar (2006)
      Traditional geostatistical estimation techniques have been used predominantly in the mining industry for the purpose of ore reserve estimation. Determination of mineral reserve has always posed considerable challenge to mining engineers due to geological complexities that are generally associated with the phenomenon of ore body formation. Considerable research over the years has resulted in the development of a number of state-of-the-art methods for the task of predictive spatial mapping such as ore reserve estimation. Recent advances in the use of the machine learning algorithms (MLA) have provided a new approach to solve the age-old problem. Therefore, this thesis is focused on the use of two MLA, viz. the neural network (NN) and support vector machine (SVM), for the purpose of ore reserve estimation. Application of the MLA have been elaborated with two complex drill hole datasets. The first dataset is a placer gold drill hole data characterized by high degree of spatial variability, sparseness and noise while the second dataset is obtained from a continuous lode deposit. The application and success of the models developed using these MLA for the purpose of ore reserve estimation depends to a large extent on the data subsets on which they are trained and subsequently on the selection of the appropriate model parameters. The model data subsets obtained by random data division are not desirable in sparse data conditions as it usually results in statistically dissimilar subsets, thereby reducing their applicability. Therefore, an ideal technique for data subdivision has been suggested in the thesis. Additionally, issues pertaining to the optimum model development have also been discussed. To investigate the accuracy and the applicability of the MLA for ore reserve estimation, their generalization ability was compared with the geostatistical ordinary kriging (OK) method. The analysis of Mean Square Error (MSE), Mean Absolute Error (MAE), Mean Error (ME) and the coefficient of determination (R2) as the indices of the model performance indicated that they may significantly improve the predictive ability and thereby reduce the inherent risk in ore reserve estimation.
    • Predictive semi-empirical analysis for tire/snow interaction

      Sankapalli, Naveen Kumar; Lin, Chuen-Sen; Liu, Qing; Zhang, Tinggang; Lee, Jonah (2004-12)
      A semi-analytical method is presented to predict the shear stress and motion resistance at the tire/snow interaction. The shear stress model is a function of normal pressure and slip. The main goal was to develop a simplified model by reducing the number of parameters in the model, so that the computational time could be reduced towards real time simulations. Motion resistance is calculated by integrating the horizontal component of normal pressure along the tire/terrain contact surface. The motion resistance obtained is slip dependent because the sinkage is a function of slip. The calculations of motion resistance and sinkage were done using the presented model and an existing model. Also the calculated results were compared with the FEA (Finite Element Analysis) data, which matched reasonably well. In the second part of the thesis shear force is expressed as a function of normal load, slip and slip angle. Shear force parameters tire stiffness, friction coefficients, and contact pressure constants were assumed as the functions of normal load and the coefficients of parameters were found through curve fitting using FEA data. These functions were used to calculate tire stiffness, friction coefficient and contact pressure constant. The calculated results matched well with FEA simulation results for the same tire and snow conditions. Pure shear force and the combined shear force were compared, and the pure shear force is always greater than the combined shear force for the same slip and slip angle.
    • Predictors of success at a rural juvenile offender facility

      Ebbesson, Gunnar Sven Ebbe (2002-08)
      Although risk factors contributing to failure in treatment of young offenders have been studied extensively, little is written about what effects success. This study on the latter takes advantage of data obtained at a local treatment facility. This study uses statistical strategies to compare 7 different variables from a set of archival data with the outcome variable, which is 'success in treatment'. The seven independent variables are ethnicity, age at entry to treatment, pre-release pass (PRP), days in treatment, FAS/FAE, sexual offender, and psychiatric diagnosis. This data has been accumulated by a clinician at the facility and offered to the investigator for the purpose of this project. The first stage of the analysis was to correlate all of the 7 variables with the outcome variable (success/no success). The variables with the strongest association were selected, and then correlated with each other. Variables shown to be correlated with success were further studied using a Logistic Regression analysis. The results of the statistical analysis showed that non-minority status was the only variable to be clearly associated with success.
    • Prefledging survival and reproductive strategies in black brant

      Flint, Paul Leroy; Sedinger, James S. (1993)
      We develop a general model useful for estimating survival of young waterfowl between hatching and fledging. Our model allows for interchange of individuals among broods and relaxes the assumption that individuals within broods have independent survival probabilities. We consider point estimation of survival rates and corresponding variances of the point estimators. We estimated gosling survival of black brant (Branta bernicla nigricans) during summers of 1987-89 on the Yukon-Kuskokwim Delta, Alaska. Eight-two percent of females radio-marked at hatch fledged at least 1 gosling (brood success). Survival of goslings within broods was estimated by 3 methods: (1) changes in mean brood size through time, (2) observation of goslings associated with marked adults, and (3) age ratios of brant captured in banding drives. Estimates of survival within successful broods averaged 77% and ranged from 57 to 90%. Combining brood success and survival of young within broods yields estimates of overall gosling survival which averaged 64% and ranged from 77% in 1987 to 52% in 1989. We analyzed variation in egg size of black brant in relation to clutch size, laying date, female age, year, and position in the laying sequence. Egg size increased with clutch size and female age, and decreased with laying date, year, and position in the laying sequence. We did not detect a negative phenotypic correlation between clutch size and egg size. However, overlap in total clutch volumes for clutches of different sizes indicated trade offs occurred among individuals with comparable investments in their clutches. We web-tagged black brant goslings at hatch, recorded their egg size, position in the egg-laying sequence, initial brood size, hatch date, and nesting density and examined the effect of these characteristics on their probability of recapture. Larger broods from larger eggs, and with earlier hatch dates were more likely to be recaptured. There was a tendency for young females to be less successful in rearing their broods; however, this may be related to their egg size, initial brood size, and hatch date, rather than age per se.
    • Prehistoric toolstone procurement and land use in the Tangle Lakes Region, central Alaska

      Lawler, Brooks A.; Potter, Ben A.; Reuther, Joshua D.; Newberry, Rainer; Hemphill, Brian (2019-05)
      This project explores prehistoric human mobility and landscape use in the Tangle Lakes region, central Alaska through analyses of toolstone procurement and manufacture conditioned by site function. Early Holocene Denali and middle Holocene Northern Archaic traditions are hypothesized to have different tool typologies, subsistence economies, and land use strategies. However, few large, systematic studies of toolstone procurement and use have been conducted. At a methodological level, archaeologists have struggled to quantitatively source non-igneous cryptocrystalline toolstone which often makes up the largest proportion of archaeological lithic assemblages. These problems were addressed by developing rigorous chemical methods for statistically assigning lithic from Tangle Lakes assemblages to (a) two known local toolstone quarries, (b) materials within the Tangle Lakes region, and (c) non-local materials. Lithic technological and geospatial analyses were used to evaluate toolstone procurement, manufacture, and use within sites. Lithic samples from four archaeological components located at different distances from their nearest known quarry sources were used to address the research problems. The archaeological samples were derived from a Denali complex hunting site (Whitmore Ridge Component 1) and three Northern Archaic assemblages: a residential site (XMH-35), a tool production site (Landmark Gap Trail) and a hunting camp (Whitmore Ridge Component 2). Chemical results indicate that cryptocrystalline material in Tangle Lakes assemblages can be statistically assigned to primary sources locations, and visual sourcing of this material is entirely unreliable. Lithic analytical results indicate that despite slight changes in mobility strategies for Denali and Northern Archaic populations, site function is the strongest conditioning factor for material selection and procurement strategies local to the Tangle Lakes region. Thus, this research provides (a) best practice methods for sourcing abundance cryptocrystalline material that has been precluded from most lithic sourcing studies, and (b) the data necessary to incorporate technological organization strategies of Tangle Lakes populations into the broader context of Denali and Northern Archaic behavioral patterns in Alaska.
    • Preliminary assessment of effectiveness of precut technique in controlling transverse cracks for asphalt pavement in Interior Alaska

      Netardus, John Jaro; Liu, Juanyu; Zhang, Xiong; Shur, Yuri; Saboundjian, Steve (2016-05)
      Transverse thermal cracking is one of the most common pavement distresses on asphalt pavements in cold climates. Transverse cracks are costly to maintain and unpleasant to drive over. The State of Alaska Department of Transportation and Public Facilities must seal cracks every summer to prevent further road damage from occurring. A simple solution that is gaining support is the precut technique where saw cuts are installed perpendicular to the road centerline shortly after construction to help relieve thermal stresses that cause cracking. This technique has effectively reduced the effects of natural transverse thermal cracking in other states as well as in Fairbanks, Alaska. This study investigates two road construction projects that include precuts with variable factors including three precut spacing intervals, five precut depths, and five pavement structures. Costs to install precuts are also compared against the cost to maintain a section without precuts in a preliminary cost effective analysis. Crack survey data from both projects have revealed that precutting does reduce transverse thermal cracking. Shorter precut spacing, placing precuts where natural cracks existed prior to construction, deeper precuts, and stronger pavement structures provided the best results. Further observations and more accurate cost data are recommended for an absolute determination of cost effectiveness.
    • Preparing Culturally Responsive Teachers Of Science, Technology, Engineering, And Math Using The Geophysical Institute Framework For Professional Development In Alaska

      Berry Bertram, Kathryn; Barnhardt, Raymond; McMillan, Claude III; Kramm, Gerhard; Smith, Roger (2011)
      The Geophysical Institute (GI) Framework for Professional Development was designed to prepare culturally responsive teachers of science, technology, engineering, and math (STEM). Professional development programs based on the framework are created for rural Alaskan teachers who instruct diverse classrooms that include indigenous students. This dissertation was written in response to the question, "Under what circumstances is the GI Framework for Professional Development effective in preparing culturally responsive teachers of science, technology, engineering, and math?" Research was conducted on two professional development programs based on the GI Framework: the Arctic Climate Modeling Program (ACMP) and the Science Teacher Education Program (STEP). Both programs were created by backward design to student learning goals aligned with Alaska standards and rooted in principles of indigenous ideology. Both were created with input from Alaska Native cultural knowledge bearers, Arctic scientists, education researchers, school administrators, and master teachers with extensive instructional experience. Both provide integrated instruction reflective of authentic Arctic research practices, and training in diverse methods shown to increase indigenous student STEM engagement. While based on the same framework, these programs were chosen for research because they offer distinctly different training venues for K-12 teachers. STEP offered two-week summer institutes on the UAF campus for more than 175 teachers from 33 Alaska school districts. By contrast, ACMP served 165 teachers from one rural Alaska school district along the Bering Strait. Due to challenges in making professional development opportunities accessible to all teachers in this geographically isolated district, ACMP offered a year-round mix of in-person, long-distance, online, and local training. Discussion centers on a comparison of the strategies used by each program to address GI Framework cornerstones, on methodologies used to conduct program research, and on findings obtained. Research indicates that in both situations the GI Framework for Professional Development was effective in preparing culturally responsive STEM teachers. Implications of these findings and recommendations for future research are discussed in the conclusion.
    • The President's Commission on Pornography

      Vorro, Amy E. (2006-05)
      The poems in this collection reflect various forms of maturation and their parallels with historic cultural shifts, specifically those typified in pop culture by the perceived climate of the 1970's. The poems contained in the first section, Deep Throat, focus on moments, taking the variables of place and sexuality heavily into account so as to explore 'the unmentionable' and their resonances for both the specifically female and generally human conditions, while simultaneously examining the personal implications. Debbie Does Dallas, the second section, continues along this vein, yet branches out to contemplate more imagined encounters and more specific taboos, sometimes through the use of traditional poetic forms. The third and final section, Behind the Green Door, steps through a doorway into the past: applying the same topics of maturation, taboos and sexuality to family structure, childhood and memory. The President's Commission on Pornography relies heavily on eccentric juxtaposition so as to stretch and investigate the amorphous boundaries of taboos, language and sexuality
    • Prestocking assessment of the prevalence and intensity of Diphyllobothrium ditremum (Creplin) plerocercoids in freshwater barriered lakes in Alaska

      Weiland, Keith Alan (1989-05)
      Plerocercoids of the pseudophyllidean cestode Diphyllobothrium ditremum (Creplin, 1825) have significantly affected the success of using certain barriered lakes for the rearing, overwintering and smolting of juvenile coho (Oncorhynchus kisutch) and Chinook (Oncorhynchus tshawytscha) salmon by causing mass mortalities of these host fishes. The prevalence of cestode procercoids in copepods, the first intermediate host, was propose as a method for assessing the potential for cestode caused losses of salmon prior to stocking a lake. However, no procercoids were found in a total of 15,276 Diaptomus and 435 Cyclops spp. from three lakes on south Baranof Island examined for procercoids. Diaptomus kenai is suggested as the first intermediate host for Diphyllobothrium ditremum. despite the absence of procercoids in any specimens examined. Diaptomus kenai was the predominant copepod in the three lakes studied, and was the prey item occurring most frequently (percent occurrence, 73.7%) in the stomach contents of 95 resident coho. Coho, Chinook, and rainbow trout (Salmo gairdneri) were obvious second intermediate hosts of D. ditremum. Among three species of piscivorous birds examined from the lake sites, a single common merganser (Merqus merganser) contained seven mature worms resembling D. ditremum. A bioassay study using coho salmon fingerlings in net pens suspended within a "cestode infested" lake proved successful as an assessment method. Plerocercoids of D. ditremum were observed in 91% of the planted coho within twenty days of exposure in Osprey Lake. Coho mortalities of 46.2% and 22.4% were observed in two pens. Mean plerocercoid intensities for apparently normal, moribund, and dead coho were 11, 28, and 32 respectively. Moribund and dead coho each had significantly larger worm loads than apparently normal coho. Primary lesions observed from gross and histopathological examinations of parasitized coho from Elfendahl and Osprey lakes included: ascites with marked distension of the abdomen; hemorrhaging of viscera primarily adipose tissue and liver; and focal necrosis of organs from migrating plerocercoids.
    • Pretreatment of aqueous phase of mine plant tailings for submarine disposal

      Choudhury, Abhishek; Bandopadhyay, Sukumar; Lin, Steve; Schiewer, Silke; Ganguli, Rajive; Wilson, Terril E. (2005-12)
      Submarine disposal of mine tailings is a relatively recent technology that holds the promise of solving the recurring problems that the mining industry has had with tailings disposal. The system has been successfully implemented in many mines around the world. Before implementation, however, a decision needs to be made whether the biogeochemical characteristics of the area selected for submarine disposal and characteristics of the tailings are conducive to implement submarine disposal of tailings. While an expert system can decide the feasibility of submarine tailings disposal (STD) based on its database of information and decision loops for the critical factors, tailings cannot be disposed of under water without pretreatment, which is the focus of this thesis. Bioremediation, freeze concentration and reverse osmosis were examined as possible alternatives for treatment. Laboratory tests were performed for all the methods, and in the case of bioremediation, pilot scale tests were also performed. It was concluded that all the three methods remove dissolved metals from mine water to varying degrees. Reverse osmosis was found to be the most efficient method, while freeze concentration was the least efficient method.
    • Preventing recidivism by using the theory of reintegrative shaming with conferences

      Enters, Patrick G.; Jarrett, Brian; Daku, Michael; Duke, J. Robert; May, Jeff (2013-06)
      Driving while intoxicated in the United States is a major problem with more than 31 percent of national driving fatalities caused by intoxicated drivers. The purpose of the present study is to identify the possibility between the use of reintegrative shaming with conferences and the likelihood that it will reduce the recidivism of driving while intoxicated. The study explores John Brathwaite's theory on reintegrative shaming and how that theory applies in conferences. The emerging theory o f Storylines from Robert Agnew is also explored in its importance when conducting these conferences. Studies conducted in Australia, Pennsylvania, Kansas and Alaska have all suggested that the use of conferences, especially those which utilize reintegrative shaming and reintegrating offenders back into the community reduces the recidivism rates. The research found in this article helps point future studies to examine offenders in a longer term after they have completed reintegrative shaming programs and conferences.
    • Prey consumption by juvenile salmonids on the Taku River, southeast Alaska

      Brownlee, Kevin (1991-05)
      Stomach contents were collected from juvenile salmonids (genus Oncorhynchus and Salvelinus) from habitats on the Taku River in 1987. Differences were defined between groups of fry. A linear discriminant function (LDF) analysis was applied to prey frequencies grouped by species, habitat, and period. The analysis discriminated between: fish in beaver ponds; sockeye in side-slough sites and fish from other mainstem sites; and beaver ponds and mainstem sites. An exclusion experiment was established in a beaver pond. The diet of sockeye (O. nerka) and coho (O. kisutch) fry was sampled from allopatric and sympatric treatment enclosures. LDF analysis applied to prey categories assigned group membership between species, treatment, and period factors. A log-linear analysis yielded significant interaction effects between the treatment, habitat, and. period explanatory variables and the response, prey, confirming the influence of the presence of cogenerics on prey consumed.
    • Prey relationships between juvenile pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon in Prince William Sound, Alaska

      Barnard, David (1981-05)
      The food relationships between juvenile pink salmon (Oncorhynchus gorbusaha) and chum salmon (O. keta) released from a hatchery Prince William Sound are examined. Samples of zooplankton and salmon fry were collected from nearshore waters adjacent to the hatchery. Salmon fry in this area have little opportunity for spatial segregation by habitat and are obliged to use common food resources. An electivity index shows that both salmon fry species selectively prey upon available zooplankton. The diets of the two salmon species are compared using a measure of overlap, Cλ, which is calculated using numerical (percent number) and mass (percent dry weight) data from stomach analyses. Values of Cλ calculated from numerical data show a moderate degree of food overlap. Values of Cλ calculated from mass data, however, show less overlap. It is concluded that on a basis of diet biomass, these two species of salmon fry effectively partition food resources.
    • Prey selectivity and diet overlap in juvenile pink, chum and sockeye salmon in the Gulf of Alaska and Prince William Sound, Alaska

      Blikshteyn, Mikhail A. (2005-12)
      Pink, chum and sockeye salmon are the three most commercially important Pacific salmon. As juveniles, they co-occur in coastal waters of Alaska. To assess the potential for competition among juveniles of these species, I examined their diets in Prince William Sound and in nearby continental shelf waters in the summer and fall of 2001 and quantified surface zooplankton at the same sampling stations. I estimated diet diversity, diet overlap and prey selectivity of the three species. A large proportion of gelatinous prey, especially larvaceans, characterized juvenile chum salmon diet. A pteropod, Limacina sp., was an important prey for juvenile pink and sockeye salmon. Juvenile pink and sockeye salmon diets consisted of a wider variety of prey than those of chum salmon; they also had a higher prey overlap with each other than with chum salmon. The three species showed similar trends in selectivity in Prince William Sound and in shelf waters. These results suggest that there is a higher probability of competition between juvenile pink and sockeye salmon than between either juvenile pink or sockeye salmon and chum salmon.
    • Price credit and price risk simulation for Alaska natural gas pipleline project

      Cao, Yue (2003-05)
      This work describes the price risk involved in developing an Alaska Natural Gas Pipeline. Three alternatives were developed. They are an ALCAN Only 4.5 Bcf/day case, a Y-line case, and an ALCAN Only 5.5 Bcf/day case. The simulation result supports the conclusion that the ALCAN Only 4.5 Bcf/day case would be the most feasible and flexible choice for the long-run gas development with less commodity risk. Also, the price credit simulation was run based on the EIA natural gas price forecast. It shows how a Federal Tax Credit helps to reduce price risk making this marginal project more acceptable for participating oil companies. However it might not be revenue neutral for the Federal Government. The risk-assessment model was constructed in the Excel spreadsheet with a commercially purchased add-in feature (@RISK by Palisade Corp.) that performed the Monte Carlo simulation and the probabilistic outcomes. It was designed to be a dynamic tool that could estimate production performance with associated costs, and product prices to Yield an economic analysis. The model was specifically designed for the Alaska Natural Gas Pipeline. This work could be useful for government, companies, and any individual, who is currently involved with the Alaska Natural Gas Act.
    • Primary afferent projections in a diver, the muskrat

      Delisa, Susan Manette; Ebbesson, S. O. E. (1989)
      In a preliminary search for primary afferent connections involved in the diving response, cutaneous afferents from the nose were traced in muskrats and compared with those in rats, and with projections from the soft palate, posterior pharynx and larynx. Horseradish peroxidase (HRP) was injected into the skin or mucosa, under anesthesia. After 48 h survival, the deeply anesthetized animal was transcardially perfused and the brain was frozen and sectioned transversely in a cryostat. The sections were reacted for HRP according to standard techniques, using tetramethylbenzidine; alternate sections were Nissl stained. HRP-labeled structures were mapped using darkfield photomicrographs and camera lucida drawings. Cutaneous afferents from the nose in the muskrat project densely to layers I-II of the ventral and dorsolateral parts of the caudal subnucleus of the spinal trigeminal nucleus (Sp5C) and sparsely to layers V-VI of Sp5C, sparsely to the ventromedial part of the interpolar subnucleus of the spinal trigeminal nucleus (Sp5I), moderately to the oral subnucleus of the spinal trigeminal nucleus (Sp5O)--particularly the dorsomedial part, possibly overlapping with the nucleus of the solitary tract, and with processes of labeled cells of other lateral facial nucleus extending into ventromedial Sp5O,--moderately to the principal trigeminal nucleus (Pr5); and to the paratrigeminal nucleus (Pa5). Projections in the rat were the same, except that little or no labeling of layers V-VI of Sp5C, dorsomedial Sp5O, or Pa5 was present. Projections from the soft palate to layers I-II of rostral Sp5C, Sp5O, Sp5I, and Pr5 were similar to those from the nose in the muskrat. Heavy projections from the soft palate, and less dense projections from the posterior pharynx and larynx, to Pa5 also were found. Those regions receiving dense projections from the nose, overlapping projections from the various sites, and more highly developed projections from the nose in the muskrat than in the rat, are of particular interest for further investigation of the neural substrate underlying the diving response. The projections traced from the nose correspond particularly with nociceptive and thermoreceptive projections, which suggests that thermoafferent function may be involved in the elicitation of the diving response.
    • Primary production and nutrient dynamics of the southeastern Bering Sea shelf

      Rho, TaeKeun (2004-05)
      Understanding the relationships between the distributions of organisms and oceanographic conditions was one of the major goals of the Southeastern Bering Sea Carrying Capacity (SEBSCC) study. As a part of SEBSCC, this study focused on the response of nutrients and primary production to the variations of physical conditions, the general distribution of primary production, and the dynamics of phytoplankton growth, and nutrient utilization over the middle shelf and shelf break regions. The concentration of nutrients and primary productivity were measured over the shelf during 1997-1999. Shipboard nutrient and iron addition experiments were conducted over the middle shelf and shelf break region of the southeastern Bering Sea shelf during 2000-2001. The variations in physical conditions strongly affected the distribution of nutrients in the surface euphotic layer as well as in the deep layer. The offshore transport of the middle shelf water at mid-depth over the outer shelf may playa very important role in the export of materials, including regenerated iron, from the middle shelf to the shelf break. There were large seasonal and spatial variations in the development of the spring phytoplankton bloom due to the strength of upwelling and the slope of the front at the shelf break. However, annual primary production, estimated by combining carbon uptake data of the PROBES study and this study, were similar over the inner (133 g C m⁻² y⁻¹), middle (144 g C m⁻² y⁻¹) and outer (138 g C m⁻² y⁻¹) shelves and the shelfbreak (143 g C m⁻² y⁻¹). Nutrient addition studies showed that nitrogen availability was essential to continuous phytoplankton growth during summer, and that the interaction between ammonium and nitrate may play an important role in the dynamics of nutrient utilization. The iron addition study suggested that lack of iron did not affect the growth of phytoplankton over the middle shelf, but slightly suppressed growth at the outside edge of the shelf break region.
    • Principal stress orientations inferred from inversion of focal mechanism data in Hawaii and Iran

      Gillard, Dominique Gerard; Wyss, Max (1993)
      Fault plane solutions were inverted to estimate stress tensor directions in Hawaii and Iran. These directions were compared to the seismically released strain tensor obtained by summing the moment tensors of the same earthquakes. Attempts were made to determine which of the nodal planes was the fault plane. Regional seismotectonic models were constructed based on these results. The seismotectonic model for west Hawaii explains the seaward motion of the upper crust along a near-horizontal plane under a near-vertical greatest principal stress. The focal mechanism of the 1951 M = 6.9 Kona earthquake in west Hawaii was modeled as a decollement based on a synthesis of teleseismic body waves using a new method designed for sparse data sets. In southeast Hawaii, a single stress tensor orientation is compatible with a complex mixture of decollement, reverse, and normal faults. However, the stress field varies as a function of space and time. The differences between stress and strain orientations are caused by rotations of stress or strain directions, respectively, while the other remains constant. A rotation of the greatest principal stress in 1979 suggests magma movements within the aseismic part of Kilauea's southeast rift zone. Strain directions rotate due to the shifting of seismic activity from one fault to another in a volume of diverse faulting. These results show that the decollement plane at 10 km depth is weak and can slip in response to greatest principal stresses oriented near-perpendicular, sub-parallel or at 45$\sp\circ$ to it. In Iran, stress directions, as estimated from major earthquakes, are homogeneous over areas several hundred kilometers long and mostly coincide with strain directions, suggesting that the strength of the crust is uniform. The quality of the stress inversion results, measured by the size of the average misfit, is similar in Hawaii and Iran, although the dimensions of the study areas vary from tens to several hundreds of kilometers, and the magnitudes of the earthquakes from M = 3.5 $\pm$ 0.5 to M = 6 $\pm$ 0.5, respectively. Average misfits between 2$\sp\circ$ and 6$\sp\circ$ were obtained in both studies and are interpreted as characteristic of crustal volumes with homogeneous stress fields.
    • Probabilistic decline curve analysis in unconventional reservoirs using Bayesian and approximate Bayesian inference

      Korde, Anand A.; Awoleke, Obadare; Goddard, Scott; Dandekar, Abhijit (2019-08)
      In this work, a probabilistic methodology for Decline Curve Analysis (DCA) in unconventional reservoirs is presented using a combination of Bayesian statistical methods and deterministic models. Accurate reserve estimation and uncertainty quantification are the primary objectives of this study. The Bayesian inferencing techniques described in this work utilizes three sampling mechanisms, namely the Gibbs Sampling (implemented in OpenBUGS), the Metropolis Algorithm, and Approximate Bayesian Computation (ABC) to sample parameter values from their posterior distributions. These different sampling mechanisms are applied in conjunction with DCA models like Arps, Power Law Exponential (PLE), Stretched Exponential Production Decline (SEPD), Duong and Logistic Growth Analysis (LGA) to estimate prediction intervals. Production is forecasted, and uncertainty bounds are established using these prediction intervals. A complete workflow and the summary steps for each of the sampling techniques are provided to permit readers to replicate results. To examine the reliability, the methodology was tested over 74 oil and gas wells located in the three main sub plays of the Permian Basin, namely, the Delaware play, the Central Basin Platform, and the Midland play. Results show that the examined DCA-Bayesian models are successful in providing a high coverage rate, low production prediction errors and narrow uncertainty bounds for the production history data sets. The methodology was also successfully applied to unconventional reservoirs with as low as 6 months of available production history. Depending on the amount of production history available, the combined deterministic-stochastic model that provides the best fit can vary. It is therefore recommended that all possible combinations of the deterministic and stochastic models be applied to the available production history data. This is in order to obtain more confidence in the conclusions related to the reserve estimates and uncertainty bounds. The novelty of this methodology relies in using multiple combinations of DCA-Bayesian models to achieve accurate reserve estimates and narrow uncertainty bounds. The paper can help assess shale plays as most of the shale plays are in the early stages of production when the reserve estimations are carried out.