The racking performance of light-frame shear walls subjected to monotonic and cyclic loading is the focus of this thesis. The sheathing materials investigated are oriented strandboard (OSB), hardboard, fiberboard, and gypsum wallboard. The objectives of this study were to (1) obtain and compare performance characteristics of each sheathing material; (2) compare the effects of monotonic loading versus the cyclic loading response; (3) investigate the contribution of gypsum in walls with dissimilar sheathing materials on opposite sides of the wall; and (4) study the effects of using overturning anchors. The monotonic tests, which incorporated the use of hold-downs, were performed according to ASTM E564. Half of the cyclic tests were performed with hold-downs, and half were performed without hold-downs. The cyclic tests were performed according to the recently adopted cyclic testing procedure ASTM E2126. A total of forty-five walls were tested with various configurations. The size of the walls was 1.2 x 2.4m (4 x 8ft). Two tests were performed with each sheathing material subjected to each type of loading: monotonic, cyclic with hold-downs, and cyclic without hold-downs. Two tests were then performed with OSB, hardboard, or fiberboard on one side of the wall and gypsum on the other side of the wall to study the effects of using dissimilar sheathing materials on the shear walls. The OSB and hardboard exhibited similar performance, and were the strongest of the four sheathing materials. Fiberboard performed better than gypsum, but worse than OSB and hardboard. In general, the performance indicators decreased when the walls were subjected to cyclic loading. The contribution of gypsum to walls with hold-downs was significant, but was not linearly additive. The use of hold-downs had a large effect on the performance of the walls. All shear wall performance indicators decreased when hold-downs were not included, with an average reduction of 66% in the peak load. / Master of Science

In this investigation, thirty-six shear walls measuring 8 feet (2.4 m) in width and possessing heights of 8, 9 and 10 feet (2.4, 2.7 and 3.0 m) were subjected to the reversed, cyclic loading schedule of the standard CUREE protocol in order to determine the performance capabilities of shear walls greater than 8 feet (2.4 m) in height sheathed with long panels. Of the thirty-six walls, a total of twelve walls measuring 9 and 10 feet (2.7 and 3.0 m) in height were sheathed with 4 x 8 feet (1.2 x 2.4 m) panels which required additional blocking members between the studs of the frame. Values obtained from the tests performed on these walls provided a direct comparison to those obtained from the walls of equal height, but sheathed with a long panel capable of spanning the entire height of the wall. The capabilities of long panels were investigated when used as the sheathing elements of shear walls with and without a mechanical hold-down device attached to the base of the end stud. An advantage of the long panel was investigated in which it was extended past the bottom plate and down onto the band joist to determine if significant resistance to the uplift present in walls without mechanical hold-down devices could be provided. Also, the effects of orienting the fibers of a 4 x 9 feet (1.2 x 2.7 m) panel in the alternate direction were examined. Average values of the parameters produced by walls sheathed with long panels either matched or exceeded those of its counterpart sheathed with 4 x 8 feet (1.2 x 2.4 m) panels in all configurations except the 10 feet (3.0 m) tall wall without hold-down devices. In fact, 4 x 9 feet (1.2 x 2.7 m) panels increased the performance of 9 feet (2.7 m) tall walls equipped with hold-down restraint significantly. Extending the long panels past the bottom plate and down onto the band joist improved the performance of both 8 and 9 feet (2.4 and 2.7 m) tall prescriptive shear walls significantly. Walls sheathed with panels made of fibers oriented in the alternate direction performed identically to those sheathed with panels of typical fiber orientation until the point of peak load. Once peak load was reached, walls sheathed with panels of alternate oriented fibers failed in a more sudden and brittle manner. / Master of Science

This thesis presents the results of testing to determine the significance of the group action factor at the 5% offset yield and capacity of single-shear bolted wood connections loaded parallel to grain. The single and multiple-bolt connections tested represent common connection geometries used in wood construction in the United States. The results of both monotonic and cyclic loading of connections are presented. Monotonic test data was used to determine an appropriately scaled CUREE Displacement Controlled Quasi-Static Cyclic Protocol. Overall, one hundred and eighty connections were tested using this cyclic protocol based on data obtained from thirty-three monotonic tests. Tested assemblies had geometric variables that include number of bolts per row, number of rows, bolt diameter, and side member material. In addition, the main and side member material and thickness were designed to produce three of the four major connection yield modes as defined by the 1997 National Design Specification for Wood Construction (AF&PA, 1997). Results from this research address the need for adequate spacing of bolts in a row to control the brittle connection behavior that directly affected the group action factor at capacity. / Master of Science

The majority of the physical properties of tissue depend directly on the interstitial or intracellular concentration of water within the epidermal and dermal layers. The relationship between skin constituent concentrations, such as water and protein, and the mechanical and optical properties of human skin is important to understand its complex nature. Localized mechanical loading has been proven to alter optical properties of tissue, but the mechanisms by which it is accomplished have not been studied in depth. In this thesis, skin's complex nature is investigated experimentally and computationally to give us better insight on how localized mechanical loading changes tissues water content and its optical properties. Load-based compression and subsequent increased optical power transmission through tissue is accomplished to explore a relationship between localized mechanical loading and tissue optical and mechanical properties. Using Optical Coherence Tomography (OCT), modification of optical properties, such as refractive index, are observed to deduce water concentration changes in tissue due to mechanical compression. A computational finite element model is developed to correlate applied mechanical force to tissue strain and water transport. Comprehensive understanding of the underlying physical principles governing the optical property changes within skin due to water concentration variation will enable future development of applications in the engineered tissue optics field. / Master of Science

The human body is a complicated dynamic system that is difficult to model because of the numerous interactions that occur between limbs during various tasks. There are documented movement differences when assessing movement in various populations, for example, joint angle and loading symmetry differences when comparing a clinical and healthy population. Symmetry deficits can impact quality of life and in some cases have been associated with an increase in injury risk. Therefore, it is essential to understand movement and loading symmetry in healthy individuals to facilitate the identification of rehabilitation targets. The purpose of this research was to assess the impact that task type and sex have on movement variability and load symmetry in healthy younger adults. The tasks included in this study represent activities of daily living such as level walking, stair ascent, stair descent and standing up from a chair. A wireless, single-sensor in-shoe force sensor allowed for data collection in a non-laboratory setting so that peak impact force and average loading rate could be evaluated across the different daily tasks. To assess movement variability, the coefficients of variation (CV) were determined for each task. The peak impact force (PIF) did not show a significant interaction between sex and task (p=0.627) or between sexes (p=0.685). The PIF did show significant between-task differences (p < 0.001), where the highest mean CV was observed in the sit-to-stand task and the lowest CV was observed during level walking. The variation between movements could be a result of the differential motor skill required to perform the task. The average loading rate (ALR) did not show a significant interaction between sex and task (p=0.069) or between sexes (p=0.624). The average loading rate showed significant between-task differences (p < 0.001), where the highest mean CV was observed in the sit-to-stand task and the lowest CV was observed during level walking. Based on these results, differences in movement type needs to be considered when evaluating average loading rate. To assess the impact of task type on load symmetry, the absolute symmetry index was calculated for the peak impact force and the average loading rate. For both parameters, only between task differences were identified (p < 0.001) and further analysis showed that sit-to-stand was significantly different from the other three movement tasks. The acceptable threshold for a healthy level of asymmetry has been defined in a clinical population to be less than 10%. Based on a chi square analysis, the 10% threshold accurately represents 95% of the population when used to measure peak impact force in level walking, stair ascent and stair descent. However, when assessing peak impact force symmetry during sit-to-stand or assessing average loading rate symmetry between tasks, the 10% threshold does not consistently represent 95% of the population. These results indicate that a threshold for a healthy symmetry may need to be redefined for bilateral movements and that the symmetry threshold may need to be specific to the outcome measure of interest. / Master of Science / When an individual completes a task there are many options for how they accomplish the movement each of which requires the different use of motor skills, these differences in how tasks are completed are called movement variability. A better understanding of these movement differences during various tasks in a healthy population then could help prevent long term injury and allow for the development of interventions to aid in recovery following injury. One way to assess measurements of the human body is to look at symmetry. Movements that are performed on a daily basis include walking, stair ascent, stair descent and standing up from a chair are considered activities of daily living throughout literature. Therefore, it is important to simulate these daily activities to assess a healthy population. Thus, this research aims to assess the impact that the type of task being completed has on the variability of movement and load symmetry in a healthy young adult population. Data collection was performed with an in-shoe measurement device that connects via Bluetooth to an iPad. These sensors allow for data to be collected outside of a laboratory setting allowing for the collection of a wider variety of tasks. The coefficient of variation (CV) was calculated for each task. This is a measure that allows for an understanding of the standard deviation of a measure in relation to the mean of the data. Differences in peak impact force and average loading rate variability were observed between tasks. For both parameters, the sit-to-stand task had the largest variability, most likely due to this being a task that allows for the use of limbs, which provides individuals with more flexibility in how they complete the movement. To assess load symmetry between tasks, the absolute symmetry index was calculated, a value that computes a percent difference between the right and left limbs. The peak impact force symmetry of the sit-to-stand task was different from the others because it requires the loading of both limbs simultaneously, which allows individuals to preferentially load one limb versus the other when completing this task. When evaluating load symmetry, clinicians have been using a threshold of 10% when defining a healthy symmetry benchmark when evaluating injury recovery. A difference greater than 10% between limbs may suggest a higher susceptibility to injury or a lack of recovery. This study evaluated if this 10% threshold accurately represents symmetry in peak impact force and average loading rate for 95% of the participants. While the 10% threshold does accurately describe the between limb differences in walking, stair ascent and stair descent tasks, the 10% threshold does not represent the results from 95% of those in this healthy population when standing up from a chair. Further, this 10% threshold did not accurately describe the symmetry discrepancies in average loading rate for any task evaluated in this study. These results suggest that a benchmark for defining healthy symmetry may need to be redefined for some tasks and outcome measures.

NAND flash-based Solid State Devices (SSDs) provide high performance and energy efficiency and at the same time their capacity continues to grow at an unprecedented rate. As a result, SSDs are increasingly being used in high end computing systems such as supercomputing clusters. However, one of the biggest impediments to large scale deployments is the limited erase cycles in flash devices. The natural skewness in I/O workloads can results in Wear imbalance which has a significant impact on the reliability, performance as well as lifetime of the cluster. Current load balancers for storage systems are designed with a critical goal to optimize performance. Data migration techniques are used to handle wear balancing but they suffer from a huge metadata overhead and extra erasures. To overcome these problems, we propose an endurance-aware write off-loading technique (EWO) for balancing the wear across different flash-based servers with minimal extra cost. Extant wear leveling algorithms are designed for a single flash device. With the use of flash devices in enterprise server storage, the wear leveling algorithms need to take into account the variance of the wear at the cluster level. EWO exploits the out-of-place update feature of flash memory by off- loading the writes across flash servers instead of moving data across flash servers to mitigate extra-wear cost. To evenly distribute erasures to flash servers, EWO off-loads writes from the flash servers with high erase cycles to the ones with low erase cycles by first quantitatively calculating the amount of writes based on the frequency of garbage collection. To reduce metadata overhead caused by write off-loading, EWO employs a hot-slice off-loading policy to explore the trade-offs between extra-wear cost and metadata overhead. Evaluation on a 50 to 200 node SSD cluster shows that EWO outperforms data migration based wear balancing techniques, reducing up to 70% aggregate extra erase cycles while improving the write performance by up to 20% compared to data migration. / Master of Science / Exponential increase of Internet traffic mainly from emerging applications like streaming video, social networking and cloud computing has created the need for more powerful data centers. Datacenters are composed of three main components- compute, network and storage. While there have been rapid advancements in the field of compute and networking, storage technologies have not advanced as much in comparison. Traditionally, storage consists of magnetic disks with magnetic parts which are slow and consume more power. However, Solid State Disks (SSDs) offer both better performance and lower energy. With the price of these SSDs being comparable to magnetic disks, they are increasingly being used in storage clusters. However, one of the biggest drawback of SSDs is the limited program erase (P/E) cycles. There is a need to ensure the uniform wearing of blocks in a SSD. While solutions for this do exist for a single SSD device, usage of these devices in a cluster poses new problems. This work introduces EWO which is a wear balancing algorithm that balances wear in a flash storage cluster. It carried out load balancing in a flash storage cluster while incorporating the wear characteristics as a cost function. EWO carries out lazy data migration also referred to as write offloading. To alleviate the metadata overhead, the migration is performed at the slice level. To evaluate EWO, a distributed key value store emulator was built to simulate the behavior of an actual flash storage cluster.

Deadwood, characterized as both downed woody material (DWM) and standing and dead stems, i.e., snags, is a significant component of terrestrial forest ecosystems. Deadwood amount and structure may influence potential wildfire hazard by altering combustible DWM mass and creating fuel structures that increase fire intensity and spread. Deadwood is also critical to carbon storage and nutrient cycling and may vary based upon the size classes of individual deadwood pieces. Lastly, deadwood structural variability has been found to positively affect species richness in bees, salamanders, birds, and small mammals, such as shrews and woodland mice. However, in the Mid-Atlantic Piedmont, there are no accessible tools to rapidly estimate deadwood of long unmanaged second growth forests to help inform future management decisions. Management agencies within this region, such as the National Park Service, may benefit from a greater understanding of the potential factors that influence deadwood accumulation, retention, and decomposition. Therefore, a project was funded by the National Park Service to investigate deadwood dynamics at Prince William Forest Park (PRWI). From May to August 2023, a deadwood inventory was conducted using planar intercepts nested within fixed radius plots along the gradient of forest cover types, aspect, elevation, and soil orders found within PRWI. Forest cover type was significant in the generalized linear model for percent dead basal area, total DWM, fine woody material, litter, and duff mass. The Virginia pine (Pinus virginiana) forest cover type had the highest percent dead basal area and total DWM mass per hectare. Elevation, aspect, and soil order were not significantly related to percent dead basal area, total DWM, 1,000 hr, fine woody material, litter, and duff mass. Data from this study may serve as a baseline for similar second growth forests of the mid-Atlantic Piedmont. / Master of Science / Visitors to Prince William Forest Park (PRWI) in eastern Virginia have voiced concern about forest health within PRWI. The perception of a high number of standing and dead stems, or snags, and a high number of decaying logs, branches, and twigs on the ground has been a focal point for visitors. Some perceive the dead material on the ground as a potential source of fuel for wildfires. Others perceive the potential hazard to humans along trails and vistas if snags were to fall. However, snags and downed woody material, known as deadwood, are critical components of forests because they store carbon and nutrients long-term and may provide habitat and resources for many wildlife species. Many other heavily used recreation locations in the eastern US face similar deadwood and forest health challenges. To respond to this, we assessed deadwood in PRWI to determine how it may be distributed differently across the variety of landscape features that are present within the park. We found the amount of total downed and dead material on the forest floor increased as the percentage of trees that were standing and dead increased. The amount of dead material on the ground was greatest for the Virginia pine (Pinus virginiana) forest community type, whereby PRWI's stands have reached their life expectancy. Prince William Forest Park's managers and those elsewhere at similar locations throughout the eastern US may benefit from this information as they seek to evaluate the status of their resources, manage those resources, and provide thoughtful messaging to the public regarding the significance and maintenance of deadwood as an ecosystem resource.

Tissue optical clearing aims to increase the penetration depth of near-collimated light in biological tissue to enhance optical diagnostic, therapeutic, and cosmetic procedures. Previous studies have shown the effects of chemical optical clearing on tissue optical properties. Drawbacks associated with chemical clearing include the introduction of potentially toxic exogenous chemicals into the tissue, poor site targeting, as well as slow transport of the chemicals through tissue. Thus, alternative clearing methods have been investigated. Mechanical compression is one such alternative tissue optical clearing technique. The mechanisms of action of mechanical compression may be similar to those of chemical clearing, though they have yet to be investigated systematically. This research describes the design and execution of a number of procedures useful for the quantification of the tissue optical clearing effects of localized mechanical compression. The first experimental chapter presents the effects of compression on image resolution and contrast of a target imaged through ex vivo biological tissue. It was found that mechanical optical clearing allowed recovery of smaller targets at higher contrast sensitivity when compared to chemical clearing. Also, thickness-independent tissue clearing effects were observed. In the second experimental chapter, dynamic changes in tissue optical properties, namely scattering and absorption coefficients (?s' and ?a, respectively) were monitored during a controlled compression protocol using different indentation geometries. A reduction in ?s' and ?a was evident for all indentation geometries, with greater changes occurring with smaller surface area. Results indicate that localized mechanical compression may be harnessed as a minimally-invasive tissue optical clearing technique. / Master of Science

The effect of cyclic moisture infiltration on connections in light-frame wood buildings has received limited research attention. Specifically, the connections between wood-based sheathing materials (OSB, plywood) and solid wood studs are of interest. A comprehensive understanding of connection performance will enhance structure and material design, thereby improving the overall integrity and robustness of light-frame structures. The focus of this research project was to evaluate the strength and stiffness of wood-frame connections exposed to cyclic humidity conditioning. Nailed sheathing/stud connection samples were tested for lateral resistance following various periods of moisture exposure. Elastic stiffness, 5% offset yield load, maximum yield load, and failure yield were computed and analyzed using the data collected. The parameters were compared among connection specimens receiving either 0, 1, 5, 10, 15, 25, or 40 periods of cyclic moisture conditioning. In addition, the bearing resistances of the materials were investigated for application to the general dowel equations for calculating lateral connection values, the current basis for design of single dowel-type fastener connections between wood-based members. An x-ray density profilometer was used to observe the de-densification processes within the composite sheathing materials throughout the moisture conditioning regime. Results indicated moderate to extreme changes in the performance of cycled connections involving lower density sheathing materials. Higher density sheathing materials performed favorably at each cycle test period. Comparisons to the yield model were similar to the control results, but usually differed as cycling increased. Analysis of connection performance following cyclic moisture loading is a vital component in developing a holistic model for service-life prediction of nailed connections in light-frame residential construction. / Master of Science

African Americans (AA) are twice as likely as White Americans (WA) to experience diabetes-related foot amputation due to foot ulcers. Foot ulcers are often caused by high plantar pressure, and several factors can impact plantar loading. Thus, there is a need to determine if race is a significant predictor of plantar loading. Additionally, with the current state of racial health disparities there is a need to determine racial differences in research engagement and mistrust between AA and WA. Data was collected from 107 participants, aged 18-30, in this Institutional Review Board approved study. An EMED pressure-measurement system (Novel Electronics, St. Paul, MN, USA) was used to collect plantar loading data. Additional measurements collected from each participant included arch height index (AHI), standing height, gait speed, and weight. Participants also completed two surveys focused on research engagement and research mistrust. A multiple linear regression was used to test if race and other factors significantly predicted plantar loading. Non-parametric tests were used to test if there were significant differences in research engagement and mistrust between AA and WA. The analysis determined that race was a significant predictor for plantar loading, along with age, AHI, gait speed, sex, and body mass index (BMI). Additionally, it was found that research engagement practices and feelings of research mistrust differed significantly between AA and WA young adults. These findings could improve our understanding as to why AA are more likely to have diabetic foot ulcers than WA, and why AA are less likely to participate in research than WA. / M.S. / African Americans (AA) are twice as likely than White Americans (WA) to experience diabetes-related foot amputation due to foot ulcers. Foot ulcers are often caused by high plantar pressure, and several factors can alter plantar loading. Thus, there is a need to determine if race is a significant predictor of plantar loading. Additionally, with the current state of racial health disparities, there is a need to determine racial differences in research engagement and mistrust between AA and WA. Data was collected from 107 participants, aged 18-30. A pressure-measurement system was used to collect plantar loading data in seven regions of the foot during self-selected speed walking. The measurements collected from each participant, included arch height, standing height, gait speed, and weight. Participants were also asked to complete two surveys focused on research engagement and research mistrust. We used this data to evaluate if race and other factors predicted plantar loading and to compare survey responses between AA and WA. It was found that race, age, arch height, gait speed, sex, and BMI were considered significant predictor variables for plantar loading measures. Additionally, research engagement practices and feelings of research mistrust differed significantly between this younger sample of AA and WA. These findings help to improve our understanding of why AA are more likely to have diabetic foot ulcers than WA, and why AA are less likely to participate in research than WA, even as young adults.