Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item INTEGRATING OFFENDING VERSATILITY INTO THE BALANCE PERSPECTIVE OF PEER INFLUENCE(2019) Pheasant, Benjamin; McGloin, Jean M; Criminology and Criminal Justice; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The balance perspective advocates for scholars to consider peer influence as both reciprocal and relative, asserting that adolescents will alter their behavior when there is an imbalance in delinquency with a peer. McGloin (2009) found support for balance when applied to frequency of offending. There is reason to suspect that this drive for behavioral homeostasis should emerge with regard to an adolescent’s offending versatility, as well. This thesis uses the AddHealth data to explore whether adolescent alter their offending versatility to achieve behavioral “balance” with a best friend, and friendship stability moderates this relationship. The results provide support for the balance perspective and suggest that respondents alter their offending versatility to become more similar to their best friend over time.Item Multivariate Correlations: Balance Operators and Variable Localization in Ensemble Data Assimilation(2017) Thomas, Catherine; Ide, Kayo; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Localization is performed in ensemble data assimilation schemes to eliminate correlations that are contaminated by sampling error. This method is frequently necessary within numerical weather prediction (NWP) applications due to the computational constraints present, limiting the number of ensemble members to a size much smaller than the dimension of the system. The most common form of localization occurs in the spatial dimensions, reducing the correlations for points that are distant and likely dominated by sampling error. Spatial localization can introduce imbalance in the system due to the disruption of physical relationships that are dictated by gradients or column integrated quantities, which produce fast-moving gravity waves within NWP models and degrade the forecast. The first part of this dissertation explores the impact of including a balance operator within ensemble data assimilation schemes and how the type of spatial localization interacts with it. The inclusion of a balance operator allows the localization to be performed on the unbalanced portion of the correlation, preserving the balanced correlation. Two data assimilation schemes are explored: a hybrid 4D ensemble-variational (4DEnVar) scheme and a Local Ensemble Transform Kalman Filter (LETKF). Observing system simulation experiments are performed using an intermediate complexity model, SPEEDY. It is shown that localizing on the background error as in the hybrid 4DEnVar is more effective than localizing on the observation error as in the LETKF. Within the LETKF, the balance operator can only propagate information one way, for example, from streamfunction to temperature, but not vice versa as in the hybrid 4DEnVar. Many applications contain variables that are physically unrelated and should not be correlated, but contain nonzero correlations. The second part of this dissertation presents two forms of variable localization in a unified framework: observation space variable localization (VO) and model space variable localization (VM). VO restricts the impact that observations have to certain model variables. VM removes the cross-correlations during the computation of the background error covariance. VM is more computationally expensive, but it has the added advantages of not requiring knowledge of observation types and allowing a single observation to impact multiple model variables whose cross-correlations have been removed.Item MECHANISMS OF GAZE STABILITY DURING WALKING: BEHAVIORAL AND PHYSIOLOGICAL MEASURES RELATING GAZE STABILITY TO OSCILLOPSIA(2015) Anson, Eric; Jeka, John J; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Visual sensory input plays a significant role in maintaining upright posture during walking. Visual input contributes to control of head, trunk, and leg motion during walking to facilitate interaction with and avoidance of objects and individuals in the environment. The vestibular system contributes to postural control during walking and also to stabilization of the eyes during head motion which may allow for more accurate use of visual information. This dissertation reports the findings of five experiments which explore how the nervous system uses vision to control upright posture during walking and also whether the act of walking contributes to gaze stability for individuals with severe vestibular loss. In the first experiment, continuous oscillatory visual scene motion was used to probe how the use of visual input changes from standing to walking and also to determine whether the trunk motion response to visual motion was the same in the medio-lateral (ML) and anterior-posterior (AP) directions. In the second experiment, visual feedback (VFB) regarding the approximate center of mass position in the ML and AP directions was used to demonstrate that ML path stability was enhanced by concurrent visual feedback for young and older adults. In the third experiment, adults with vestibular loss and healthy adults were both able to use VFB during treadmill walking to enhance ML path stability and also to separately modify their trunk orientation to vertical. The final two experiments investigated whether gaze stability was enhanced during treadmill walking compared to passive replication of sagittal plane walking head motion (seated walking) for individuals with severe vestibular loss. Individuals with severe bilateral vestibular hypofunction displayed appropriately timed eye movements which compensated for head motion during active walking compared to seated walking. Timing information from the task of active walking may have contributed to enhancement of gaze stability that was better than predictions from passive head motion. This dissertation demonstrates: 1) the importance of visual sensory input for postural control during walking; 2) that visual information can be leveraged to modify trunk and whole body walking behavior; and 3) that the nervous system may leverage intrinsic timing information during active walking to enhance gaze stability in the presence of severe vestibular disease.