Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Methodological considerations and clinical utility of analyzing transient behavior in quiet stance postural control(Montana State University - Bozeman, College of Engineering, 2020) Reed, Cody Aaron; Chairperson, Graduate Committee: Scott Monfort; Ajit M.W. Chaudhari, Lise C. Worthen-Chaudhari, Kimberly E. Bigelow and Scott M. Monfort were co-authors of the article, 'A new perspective on transient characteristics of quiet stance postural control' in the journal 'PLOS ONE' which is contained within this thesis.; Scott M. Monfort were co-authors of the article, 'Influence of a cognitive perturbation on transient characteristics of quiet stance postural control' submitted to the journal 'Gait & posture' which is contained within this thesis.Postural control has been widely studied to provide insight into various health concerns. Traditionally, postural control is assessed using whole-trial analysis techniques that measure center of pressure parameters as a singular estimate for an entire trial. These whole-trial estimates may be more reliable for longer duration trials. However, longer trials and whole-trial analyses mask transient (i.e., a destabilized period followed by a transition to a more stable, quasi-steady state level) responses within center of pressure data. By only using whole-trial estimates, we may be missing out on unique information that is contained within this understudied aspect of postural control. Therefore, four experiments were conducted to better understand the clinical utility of evaluating transient postural control behavior. The first experiment tested whether transient, epoch-based characteristics of center of pressure parameters provided unique information compared to traditional whole-trial estimate approaches. The second experiment evaluated participants in eyes open and closed conditions to test whether transient behavior was a sensory reweighting response to eye closure. The third experiment tested whether transient characteristics of postural control could distinguish between younger and older adults. Based on the results of the first three experiments, a fourth experiment was conducted to investigate the influence of cognitive perturbations on transient characteristics of postural control. Negligible correlations were found between transient characteristic and whole-trial estimates, indicating that unique information is contained in transient measures of postural control. Although transient behavior was exaggerated during eyes closed stance, transient behavior still existed during eyes open stance. In addition, select transient characteristics distinguished between young and older adult groups, supporting the clinical relevance of transient measures. Lastly, cognitive perturbations influenced transient postural behavior, supporting the use of transient measures for analyzing dual-task scenarios. Overall, our results support the use of epoch-based estimates to characterize transient postural behavior as a complementary assessment to traditional whole-trial analyses. Our results also indicate the need to carefully consider how postural control trials are analyzed and initiated. Moving forward, further evaluation of transient characteristics of postural control is warranted to determine their relationship to health outcomes such as falls.Item Wide-area control strategies for improving transient stability in a multi-machine power systems(Montana State University - Bozeman, College of Engineering, 2020) Ojetola, Samuel Toluwanimi; Chairperson, Graduate Committee: Todd Kaiser and Josh WoldTransient stability is the ability of synchronous machines in an interconnected power system to remain in synchronism after been subjected to a large disturbance. Transient instability is one of the less probable but severe events that a power system encounter in its daily operations. Historically, it has been the dominant stability problem in power systems and has been the focus of much of the power industry's attention. Traditionally, when a generator or group of generators begin to lose synchronism with the rest of the system, they are tripped or islanded from the network to maintain transient stability and to prevent or limit cascaded outages. However, with the increase in the penetration of inverter-based generation, tripping schemes may become difficult to apply because of wide distribution of generation and loss of system inertia. This research presents control strategies that improves the transient stability of a power system without having to trip generators. This is achieved by modulating the active power absorbed or injected by distributed energy storage devices. These devices are located at the high voltage bus of several generators in a synchronous power system and are independently controlled. The strategy is based upon local and center-of-inertia frequency estimated in real time from wide-area measurements. It is shown that by absorbing or injecting real-power into a power system to remove as much kinetic energy gained during a disturbance as quickly as possible before it is converted to potential energy, synchronism can be maintained. The performance of the control strategy is evaluated on several multi-machine power system models. The result shows that this control strategy significantly improves the transient stability of power systems.Item An investigation of the spatial variability and efficacy of the Extended Column Test(Montana State University - Bozeman, College of Letters & Science, 2014) Hoyer, Ian Richard Steele; Chairperson, Graduate Committee: Jordy Hendrikx; Jordy Hendrikx, Karl W. Birkeland and Kathryn M. Irvine were co-authors of the article, 'Spatial variability of extended column test results at the slope scale' submitted to the journal 'Cold regions science and technology' which is contained within this thesis.Most avalanche accidents are the results of an avalanche triggered by the victim, or a member of the victim's party. Many of these accidents are the result of uncertainty regarding the stability of the snowpack. Spatial variability of snow stability is a significant cause of this uncertainty. There has been significant previous work on the spatial variability of snow stability at multiple spatial scales, but most of these studies have focused on measures of fracture initiation. This study investigates the spatial variability of Extended Column Test (ECT) results (an index of fracture propagation). We measured the spatial variability of ECT results in 23 grids across southwest Montana over the course of two winters. These slopes were all topographically uniform, wind sheltered clearings, with snowpacks relatively undisturbed by skiers or snowmobiles. Twenty eight ECTs were spaced across each grid in a standardized layout with a 30 m x 30 m extent. Our results are consistent with previous work, with some grids showing high levels of variability as well as other grids with relatively homogenous results. We found no consistent spatial pattern to our test results. We tested slopes with a variety of weak layers (surface hoar, depth hoar, new snow, and near surface facets), slab characteristics (slab hardness, slab depth), and snow depths and found no correlations with ECT results. We found a relationship between the forecasted regional avalanche danger and the percent of ECTs showing propagation in a grid. As the regional danger increases the percent of ECTs propagating in a grid does as well. ECT results are most variable under moderate danger. When the regional avalanche danger is either considerable or low, results are likely to be more consistent. The key practical implication of our results is that ECTs, like all other stability tests, should be interpreted with an appropriate level of caution and in consideration of all other relevant variables. The spatial variability of this test has the potential to be high on some slopes, while on other slopes test results will be entirely in agreement.