Now showing items 41-60 of 6376

• #### A nested watershed study in the Kuparuk River basin, arctic Alaska: Streamflow, scaling, and drainage basin structure

The central hypothesis of this dissertation is that permafrost influences the form, function, and scaling of hydrologic and geomorphologic characteristics in the Kuparuk River basin in Northern Alaska. This problem was addressed using three approaches: field hydrologic studies, statistical scaling studies, and geomorphology studies using digital elevation models. Permafrost and snow exert significant controls on hydrologic processes in the Kuparuk River basin. Storm hydrographs show fast responses, long time lags, extended recessions, and high runoff/precipitation ratios. These features arise from the diminished storage capacity caused by permafrost. Summer storm flow compositions in the are dominated by old water, as is commonly observed in basins without permafrost. However, the thawing active layer imposes seasonal trends on storm flow composition and other streamflow characteristics. These seasonal trends are often masked by precipitation patterns. Significant differences exist in the spatial variability and scaling of streamflow between arctic and temperate basins. Streamflow in arctic basins is subject to simple scaling, whereas streamflow in temperate regions is subject to multiscaling. Since the variability of streamflow downstream results from the timing of storm hydrographs upstream, regional scaling differences may result from the differences in runoff generation mechanisms in basins with and without permafrost. Fractal analysis of channel networks, and the scaling of mass distribution suggest that channel networks in the Kuparuk River basin are underdeveloped. Hillslope water tracks convey water off slopes, but the organization of water tracks lacks universal characteristics of mass and energy distribution common to other rivers, and hence cannot be considered fluvial channels. However, the heads of water tracks are located where some theoretical models of channel initiation predict that channels should occur. A likely scenario is that a rudimentary channel network was formed soon after deglaciation, but was never allowed to develop into a mature network due to the limits that permafrost imposes on erosion. An encompassing conclusion is that the Kuparuk River basin is adjusted to arctic conditions in both form and function. Consequently, thermal changes to the existing permafrost condition may impose significant changes in the erosional development of channel networks and in the subsequent hydrologic response.
• #### A Parent's Choice

In one rural Alaska school district, parents have a choice to place their child in an English only school or a Yup'ik immersion school. In the English only school, all subjects are taught in English. In the dual immersion school, English is introduced at third grade and progressively increases with each grade level until the sixth grade, when students exit the program. The researcher will seek to find why parents choose to place their child in the English only school or in the Yup'ik Immersion School. This inquiry is to help the researcher understand the thoughts and perceptions that are being held by parents and members in the community about each of the schools. The study will use qualitative research methodology that includes questionnaires and personal interviews to find out the thoughts and feelings that are being held by the parents. This research seeks to find the reasons why parents choose one school over the other. After reviewing the questionnaires, the researcher will select five parents from each school with various backgrounds to interview. The researcher will conduct ethnographic interviews designed to elicit more in-depth information. The interviews will be coded and emergent themes identified. Through data analysis, the researcher hopes to discover the reasons why parents are choosing each of the schools.
• #### A Search For Thermospheric Composition Perturbations Due To Vertical Winds

The thermosphere is generally in hydrostatic equilibrium, with winds blowing horizontally along stratified constant-pressure surfaces, driven by the dayside-to-nightside pressure gradient. A marked change in this paradigm resulted after Spencer et al. [1976] reported vertical wind measurements of 80 m&middot;s-1 from analyses of AE-C satellite data. It is now established that the thermosphere routinely supports large-magnitude (~30-150 m&middot;s-1) vertical winds at auroral latitudes. These vertical winds represent significant departure from hydrostatic and diffusive equilibrium, altering locally---and potentially globally---the thermosphere's and ionosphere's composition, chemistry, thermodynamics and energy budget. Because of their localized nature, large-magnitude vertical wind effects are not entirely known. This thesis presents ground-based Fabry-Perot Spectrometer OI(630.0)-nm observations of upper-thermospheric vertical winds obtained at Inuvik, NT, Canada and Poker Flat, AK. The wind measurements are compared with vertical displacement estimates at ~104 km2 horizontal spatial scales determined from a new modification to the electron transport code of Lummerzheim and Lilensten [1994] as applied to FUV-wavelength observations by POLAR spacecraft's Ultraviolet Imager [Torr et al. , 1995]. The modification, referred to as the column shift, simulates vertical wind effects such as neutral transport and disruption of diffusive equilibrium by vertically displacing the Hedin [1991] MSIS-90 [O2]/[N2] and [O]/([N2]+[O2]) mixing ratios and subsequently redistributing the O, O2, and N 2 densities used in the transport code. Column shift estimates are inferred from comparisons of UVI OI(135.6)-nm auroral observations to their corresponding modeled emission. The modeled OI(135.6)-nm brightness is determined from the modeled thermospheric response to electron precipitation and estimations of the energy flux and characteristic energy of the precipitation, which are inferred from UVI-observed Lyman-Birge-Hopfield N2 emissions in two wavelength ranges. Two-dimensional column shift maps identify the spatial morphology of thermospheric composition perturbations associated with auroral forms relative to the model thermosphere. Case-study examples and statistical analyses of the column shift data sets indicate that column shifts can be attributed to vertical winds. Unanticipated limitations associated with modeling of the OI(135.6)-nm auroral emission make absolute column shift estimates indeterminate. Insufficient knowledge of thermospheric air-parcel time histories hinders interpretations of point-to-point time series comparisons between column shifts and vertical winds.
• #### A self-consistent time varying auroral model

A time dependent model of auroral processes has been developed by self-consistently solving the electron transport equation, the ion continuity equations and the electron and ion energy equations. It is used to study the response of ionospheric and atmospheric properties in regions subjected to electron bombardment. The time history of precipitation events is computed for a variety of electron spectral energy distributions and flux magnitudes. Examples of daytime and night-time aurorae are presented. Precipitating energetic auroral electrons heat the ambient electrons and ions as well as enhancing the ionization rate which increases the ion concentration. The consequences of electric field acceleration and an inhomogeneous magnetic field in auroral electron transport in the topside ionosphere are investigated. Substantial perturbations of the low energy portion of the electron flux are produced: An upward directed electric field accelerates the downward directed flux of low energy secondary electrons and decelerates the upward directed component. Above about 400 km the inhomogeneous magnetic field produces anisotropies in the angular distribution of the electron flux. The effects of the perturbed energy distributions on auroral spectral emission features and on the electron temperature are noted. The response of the Hall and Pederson conductivities to auroral electron precipitation is discussed as a function of the characteristic energy of the spectral distribution.
• #### A simulation study of magnetic reconnection processes at the dayside magnetopause

In this thesis, the dayside reconnection processes are studied by using computer simulations. First, the global magnetic reconnection patterns at the dayside magnetopause are studied based on a two-dimensional incompressible magnetohydrodynamic (MHD) code. It is found that multiple X line reconnection may prevail at the dayside magnetopause when the magnetic Reynolds number is large ($>$200). The formation and subsequent poleward convection of magnetic islands are observed in the simulation. The Alfven Mach number of the solar wind, $M\sb{Asw}$, can also change the reconnection patterns. For a large $M\sb{Asw}$, reconnection tends to occur at the higher latitude region. Secondly, the structure of the dayside reconnection layer is studied by a two-dimensional compressible MHD simulation. In a highly asymmetric configuration typical of the dayside magnetopause, the pair of slow shocks bounding the reconnection layer in Petschek's symmetric model is found to be replaced by an intermediate shock on the magnetosheath side and a weak slow shock on the magnetospheric side. In addition, a mechanism for the enhancement of $B\sb y$, which is observed in the magnetopause current layer and magnetic flux tubes, is proposed.
• #### A simulation study of three-dimensional magnetic reconnection

The magnetic reconnection process plays an important role in the interaction between the solar wind and the magnetosphere. It leads to the transfer of energy from the solar wind into the magnetosphere. In this thesis, we study three-dimensional (3D) aspects of magnetic reconnection based on magnetohydrodynamic (MHD) simulations. First, we examine the magnetic field topology of magnetic flux ropes formed in multiple X line reconnection (MXR). It is found that the magnetic field topology depends on the relative extent and location of the two neighboring X lines. Magnetic flux ropes with either smooth or frayed ends are obtained in our simulations. For magnetic flux ropes with smooth ends, a major amount of magnetic flux is connected at each end to only one side of magnetopause. Second, the evolution of the core magnetic field in the magnetic flux tube is studied for various magnetic reconnection processes. We find that the 3D cases always lead to a larger enhancement of core field than the corresponding 2D cases since plasma can be squeezed out of the flux tube in the third direction. The MXR process gives rise to a larger increase of the core field than the single X line reconnection process. The core magnetic field can be enhanced to three times the ambient magnetic field strength in the 3D MXR process. Finally, we examine the generation and propagation of Alfven waves and field-aligned currents in the 3D reconnection process. For cases with a zero guide field, it is found that a large portion of the field-aligned currents ($\sim$40%) is located in the closed field line region. Both the pressure gradient term and inertia term contribute to the generation of field-aligned currents. For cases with nonzero guide field, one sense of field-aligned currents is dominant due to the presence of the initial field-aligned current. In these cases, the inertia term makes a major contribution to the redistribution of field-aligned currents. The influence of the initial guide field on the longitudinal shift of the current reversal site is found to be consistent with observations.
• #### A Sounding Rocket Attitude Determination Algorithm Suitable For Implementation Using Low Cost Sensors

The development of low-cost sensors has generated a corresponding movement to integrate them into many different applications. One such application is determining the rotational attitude of an object. Since many of these low-cost sensors are less accurate than their more expensive counterparts, their noisy measurements must be filtered to obtain optimum results. This work describes the development, testing, and evaluation of four filtering algorithms for the nonlinear sounding rocket attitude determination problem. Sun sensor, magnetometer, and rate sensor measurements are simulated. A quatenion formulation is used to avoid singularity problems associated with Euler angles and other three-parameter approaches. Prior to filtering, Gauss-Newton error minimization is used to reduce the six reference vector components to four quaternion components that minimize a quadratic error function. Two of the algorithms are based on the traditional extended Kalman filter (EKF) and two are based on the recently developed unscented Kalman filter (UKF). One of each incorporates rate measurements, while the others rely on differencing quaternions. All incorporate a simplified process model for state propagation allowing the algorithms to be applied to rockets with different physical characteristics, or even to other platforms. Simulated data are used to develop and test the algorithms, and each successfully estimates the attitude motion of the rocket, to varying degrees of accuracy. The UKF-based filter that incorporates rate sensor measurements demonstrates a clear performance advantage over both EKFs and the UKF without rate measurements. This is due to its superior mean and covariance propagation characteristics and the fact that differencing generates noisier rates than measuring. For one sample case, the "pointing accuracy" of the rocket spin axis is improved by approximately 39 percent over the EKF that uses rate measurements and by 40 percent over the UKF without rates. The performance of this UKF-based algorithm is evaluated under other-than-nominal conditions and proves robust with respect to data dropouts, motion other than predicted and over a wide range of sensor accuracies. This UKF-based algorithm provides a viable low cost alternative to the expensive attitude determination systems currently employed on sounding rockets.
• #### A statewide training model for supported employment using master trainers

Alaska's vast land mass and diversified urban, rural, and remote communities require innovative training curricula to meet training needs in supported employment. A competency-based training program using an independent learning format and master trainers was developed to meet these extreme needs. These training methods were evaluated with survey instruments at the time of training and at 3 months, 6 months, and 1 year follow up. The data demonstrate that the training materials as well as the independent study format and master trainer model were effective training methods. We conclude that the training methods developed are effective in meeting the diverse training needs of urban, rural, and remote sites.
• #### A study of one-dimensional nonlinear hydromagnetic waves and collisionless shocks

A variety of nonlinear hydromagnetic waves have been observed in the collisionless solar wind plasma. A comprehensive theoretical study of nonlinear hydromagnetic waves, including rotational discontinuities and collisionless shocks, is carried out in this thesis by means of both analytical solutions and numerical simulations. Nonlinear hydromagnetic waves are governed by the interplay of the dispersion process, the collisionless dissipation process and the nonlinear steepening process. The purpose of this thesis is to understand the nonlinear behavior of hydromagnetic waves in terms of these fundamental processes. It is shown that the rotational discontinuity structures observed in the solar wind and at the magnetopause are nonlinear Alfven wave solutions of the collisionless two-fluid plasma equations. In these nonlinear wave solutions, nonlinear steepening is self-consistently balanced by dispersion. Collisionless viscous dissipation is the dominant dissipation in high Mach number shocks, which converts the flow energy into thermal energy. Hybrid simulations show that the collisionless viscous dissipation can result from the reflection and pitch-angle scattering of incoming ions flowing through the magnetic structures in the shock transition region. Collisionless dissipations in hydromagnetic shocks is governed by the magnetic structures in the shock transition region. The dissipation in turn can modify the wave structures and balance the nonlinear steepening. However, such delicate balance of the dispersion, dissipation, and nonlinear steepening has been observed to break down momentarily in high Mach number quasi-parallel shocks. This leads to the so-called cyclic shock front reformation seen in the hybrid simulations. The shock front reformation can be explained in terms of momentary off-balance between the dispersion-dissipation on the one hand and the nonlinear steepening on the other hand. The off-balance occurs after a significant fraction of incoming ions are reflected. Each off-balance lasts a few ion gyro periods, which governs the shock front reformation time scale.

• #### A study of the magnetosphere-ionosphere coupling processes

Magnetosphere-ionosphere (M-I) coupling processes are studied by using numerical modeling. An M-I coupling model of substorms on the ionospheric recombination time scale (tens of seconds) is developed. The model is two-dimensional (2-D) and time-dependent from which several signatures of substorms can be obtained and understood. The model is then extended to northward interplanetary magnetic field (IMF) conditions to study the effects of the M-I coupling on the high-latitude convection. Based on the model results, a mechanism for the origin of distorted two-cell ionospheric convection is proposed. The ionospheric and ground signatures of multiple field-aligned current sheets originating from dayside flux transfer events have been modeled. The interaction between Alfven waves and field aligned potential drops is studied by using a local model.
• #### A study on the interaction of Alzheimer's disease beta amyloid protein with cultured mouse neuroblastoma cell line NB41A3

The $\beta$ amyloid protein is the primary constituent of amyloid plaques in the brains of Alzheimer's disease patients. The generation of $\beta$ amyloid protein from $\beta$ amyloid precursor protein and its interaction with neuronal cells were studied in the mouse neuroblastoma cell line NB41A3. Immunoreactivity to the carboxyl terminal of the precursor protein was detected among the membrane proteins of these cells, indicating that $\beta$ amyloid precursor protein is produced by NB41A3 cells. Also amyloid precursor protein carboxyl terminal immunoreactivity was observed in the conditioned medium of the cells, demonstrating various cytosolic peptide fragments are secreted during the cellular processing of the $\beta$ amyloid precursor protein. Synthetic $\beta$ amyloid peptide was shown to negatively affect NB41A3 neuroblastoma cells as judged by decreasing cell numbers, decreasing amount of cell protein, and release of the cytosolic enzyme, lactic dehydrogenase, into the medium. At the ultrastructural level, internal damage to the nucleus could be observed. Synthetic $\beta$ peptide showed specific binding with neuroblastoma cells. The internalization of the $\beta$ peptide into the cells suggest a direct mechanism for $\beta$ amyloid protein toxicity in vivo. This research contributes to the knowledge of the processing of Alzheimer's disease $\beta$ amyloid precursor protein in NB41A3 cells and demonstrates that NB41A3 cell provides a practical in vitro model for studying the mechanism of Alzheimer's disease and amyloid toxicity.
• #### A Synoptic Climatology Of Alaska: Winter 700Mb Height Anomaly Patterns And Surface Climate Variability, 1956-1986

An objective, descriptive study of Alaska's winter season synoptic climatology is compiled to identify regional monthly 700mb anomaly height patterns and to investigate monthly-mean surface temperature and precipitation variability during the thirty-year period from 1956/57 to 1985/86. A total of 78% of the period's monthly 700mb anomaly height maps are classified into ten Basic Anomaly Pattern categories by a Kirchhofer/Lund-based pattern classification scheme. Patterns are described in terms of frequency of occurrence, climate associations, and specific climate events (case study format). Examination of the winter monthly-mean temperature and precipitation records for the nine NOAA-designated Alaska climate divisions, and the Gulf of Alaska indicates a cool, dry period in the January record from 1964-1977. The winters following 1977 are the most variable of the thirty-year record. Seasonal-scale linear trends indicate a warmer, drier shift in the interior divisions and a warmer, wetter shift in the southern coastal divisions. <p>
• #### A temperature only formulation for ice sheets

Temperature plays an important role in the dynamics of large flowing ice masses like glaciers and ice sheets. Because of this role many models for ice sheets model temperature in some form. One type of model for polythermal glaciers (glaciers which contain both ice below, and at the pressure-melting temperature) explicitly separates the ice into distinct cold and temperate regimes, and tracks the interface between them as a surface. Other models track the enthalpy (internal energy) across both domains, with temperature being a function of enthalpy. We present an alternative mathematical formulation for polythermal glaciers and ice-sheets, in the form of a variational inequality for the temperature field only. Using the calculus of variations, we establish some sufficient conditions under which our formulation is well-posed. We then present some numerical approximations of solutions obtained via the Finite Element Method.
• #### A theoretical study of magnetosphere-ionosphere coupling processes

Magnetosphere and ionosphere are coupled electrodynamically by waves, field-aligned currents and parallel electric fields. Several fundamental coupling processes are addressed in my thesis. It is shown that the Alfven wave is the dominant mode in transmitting field-aligned currents. Therefore, dynamic M-I coupling can be modeled by the Alfven wave bouncing between the ionosphere and the magnetospheric boundaries. The open magnetopause, separating the solar wind and the magnetosphere, behaves like a near perfect reflector to the Alfven wave because of the large solar wind inertia. At the plasma sheet, however, the reflection coefficient may extend over a wide range, depending on the location in the plasma sheet. As the Alfven wave propagates back and forth between the magnetosphere and ionosphere, the field-aligned current density increases dramatically at certain locations, especially near the head of the westward traveling surge, causing potential drops to develop along magnetic field lines. It is found that the existence of parallel potential drops can distort the global convection pattern and limit the upward field-aligned current. The magnetic reconnection at the dayside magnetopause is responsible for enhancing the convection in the magnetosphere, which subsequently propagates toward the ionosphere by the Alfven wave. The patchy and intermittent reconnection at the dayside magnetopause can be initiated by the 3-D tearing instability, leading to the isolated magnetic islands and X-line segments. The nonlinear evolution of tearing in terms of the magnetic island coalescence is also studied.