Obesity is associated with an increased risk of falls and subsequent injury. Most falls result from some type of postural perturbation. As such, it is important to understand how obesity influences balance recovery from a postural perturbation. There is limited information on the effects of obesity on balance recovery, and the limited available information is ambiguous. Therefore, the purpose of the research within this dissertation was to investigate the effects of obesity on balance recovery after a postural perturbation in young adults to better understand how obesity contributes to fall risk. Four separate studies make up this dissertation. The purpose of the first study was to investigate the effects of obesity on balance recovery ability using an ankle strategy in young adults. Normal-weight and obese participants recovered balance using an ankle strategy after three types of postural perturbations: an initial angular displacement, an initial angular velocity from the natural stance, and an initial angular velocity from a prescribed position. Obese participants were unable to recover balance using an ankle strategy as well as normal-weight participants when perturbations involved an initial angular velocity. However, no differences between obese and normal-weight participants were found when perturbations only involved an initial angular displacement. The effect of obesity on balance recovery in young adults was dependent on the perturbation characteristics, and may be explained by a possible beneficial effect of increased inertia on balance recovery after perturbations with little or no initial angular velocity. The purpose of the second study was to examine the effects of obesity on balance recovery by stepping in young adults. The ankle strategy has the benefit of simplifying the mechanics of balance recovery, but limits generalizability to more realistic fall scenarios where stepping to extend the base of support and recover balance is desired. Similar to the first study, participants attempted to recover balance following two types of postural perturbations: an initial angular displacement from an upright stance (by releasing participants from a static forward lean), and an initial angular velocity while in an upright stance (using a translating platform). In contrast to the first study, the ability to recover balance with a single-step did not differ between young normal-weight and obese adults. These results suggest that the reported increase in fall risk in obese adults is not a result of impaired balance recovery ability (at least among young adults that were tested here). The third study examined the effects of obesity on body kinematics immediately following a trip-like perturbation in young adults. Obesity was found to increase body angular velocity the perturbation, and that increases in body angular velocity were associated with an increased probability of a failed recovery. These results suggest that when a young obese and young normal-weight individual trip while walking at similar speeds, the young obese individual may be at a greater risk of falling following a trip because the young obese individual will experience a greater body angular velocity. This detrimental effect of obesity on the difficulty of recovering from a trip-like perturbation in young adults is most likely due to how mass is distributed throughout the body and not the amount of mass itself. The final study examined the relationship between relative strength and functional capability in young adults, and how obesity influences this relationship. To compare relative strength used during a functional task (i.e. balance recovery from a forward fall), the obese and normal-weight individual should complete the task with identical kinematics. Forward dynamic simulations were used to address this research question, instead of human subjects testing, to achieve identical kinematics. Differences in peak relative torques were found between the normal-weight and obese model, with the largest differences seen at the hip. These findings suggest that young obese individuals use greater relative strength at some joints than young normal-weight individuals to perform the time-critical task of balance recovery, and that these differences in relative strength demands may limit functional capability in young individuals who are obese. / Ph. D.

Exploring unconventional hydrocarbon reservoirs and enhancing the recovery of hydrocarbon from conventional reservoirs are necessary for meeting the society's ever-increasing energy demand and requires a thorough understanding of the multiphase interfacial and transport phenomena in these reservoirs. This dissertation performs pore-scale studies of interfacial thermodynamics and multiphase hydrodynamics in shale reservoirs and conventional oil-brine-rock (OBR) systems. In shale gas reservoirs, the imbibition of water through surface hydration into gas-filled mica pores was found to follow the diffusive scaling law, but with an effective diffusivity much larger than the self-diffusivity of water molecules. The invasion of gas into water-filled pores with width down to 2nm occurs at a critical invasion pressure similar to that predicted by the classical capillary theories if effects of disjoining pressure and diffusiveness of water-gas interfaces are considered. The invasion of oil droplets into water-filled pores can face a free energy barrier if the pressure difference along pore is small. The computed free energy profiles are quantitatively captured by continuum theories if capillary and disjoining pressure effects are considered. Small droplets can invade a pore through thermal activation even if an energy barrier exists for its invasion. In conventional oil reservoirs, low-salinity waterflooding is an enhanced oil recovery method that relies on the modification of thin brine films in OBR systems by salinity change. A systematic study of the structure, disjoining pressure, and dynamic properties of these thin brine films was performed. As brine films are squeezed down to sub-nanometer scale, the structure of water-rock and water-oil interfaces changes marginally, but that of the electrical double layers in the films changes greatly. The disjoining pressure in the film and its response to salinity change follow the trend predicted by the DLVO theory, although the hydration and double layer forces are not simple additive as commonly assumed. A notable slip between the brine film and the oil phase can occur. The role of thin liquid films in multiphase transport in hydrocarbon reservoirs revealed here helps lay foundation for manipulating and leveraging these films to enhance hydrocarbon production and to minimize environmental damage during such extraction. / Doctor of Philosophy / Meeting the ever-increasing energy demand requires efficient extraction of hydrocarbons from unconventional reservoirs and enhanced recovery from conventional reservoirs, which necessitate a thorough understanding of the interfacial and transport phenomena involved in the extraction process. Abundant water is found in both conventional oil reservoirs and emerging hydrocarbon reservoirs such as shales. The interfacial behavior and transport of water and hydrocarbon in these systems can largely affect the oil and gas recovery process, but are not well understood, especially at pore scale. To fill in the knowledge gap on these important problems, this dissertation focuses on the pore-scale multiphase interfacial and transport phenomena in hydrocarbon reservoirs. In shales, water is found to imbibe into strongly hydrophilic nanopores even though the pore is filled with highly pressurized methane. Methane gas can invade into water-filled nanopores if its pressure exceeds a threshold value, and the thin residual water films on the pore walls significantly affect the threshold pressure. Oil droplet can invade pores narrower than their diameter, and the energy cost for their invasion can only be computed accurately if the surface forces in the thin film formed between the droplet and pore surface are considered. In conventional reservoirs, thin brine films between oil droplet and rock greatly affect the wettability of oil droplets on the rock surface and thus the effectiveness of low-salinity waterflooding. In brine films with sub-nanometer thickness, the ion distribution differs from that near isolated rock surfaces but the structure of water-brine/rock interfaces is similar to their unconfined counterparts. The disjoining pressure in thin brine films and its response to the salinity change follow the trend predicted by classical theories, but new features are also found. A notable slip between the brine film and the oil phase can occur, which can facilitate the recovery of oil from reservoirs.

Landfill leachate contains valuable, recoverable organics, water, and nutrients. This project investigated leachate treatment and resource recovery from landfill leachates by innovative methods such as forward osmosis (FO), bioelectrochemical systems (BES), and advanced oxidation. In this study, a microbial fuel cell (MFC) removed 50-75% of the ammonia from a leachate through the electricity driven movement of ammonium to the cathode chamber followed by air stripping at high pH (> 9). During this process, the MFC system removed 53-64% of the COD, producing a net energy of 0.123 kWh m-3. Similarly, an integrated microbial desalination cell (MDC) in an FO system recovered 11-64% of the ammonia from a leachate; this was affected by current generation and hydraulic retention time in the desalination chamber. The MDC-FO system recovered 51.5% of the water from a raw leachate. This increased to 83.5% when the FO concentrate was desalinated in the MDC and then recirculated through the FO unit. In addition, the project investigated humic acid (HA) recovery from leachate during the synergistic incorporation of FO, HA recovery, and Fenton's oxidation to enhance leachate treatment and to reduce Fenton's reagent requirements. This led to the investigation of harmful disinfection byproducts (DBPs) formation during Fenton's oxidation of landfill leachate. The removal of leachate UV-quenching substances (humic, fulvic, and hydrophilic acids) using an MFC and a chemical oxidant (i.e., sodium percarbonate) with a focus on energy production and cost efficiency were also studied. BES treatment can reduce leachate organics concentrations; lower UV absorbance; recover ammonia; and, in combination with FO, recover water. Although BES is promising, significant work is needed before its use in landfill leachate becomes practical. FO application to leachate treatment must consider the choice of an appropriate draw solute, which should require minimal effort for regeneration. Resources like HA in leachate deserve more attention. Further efforts can focus on purification and application of the recovered products. The emerging issue of DBP formation in leachate treatment also requires attention due to the potential environmental and human health effects. The broader impact of this study is the societal benefit from more sustainable and cost-efficient leachate treatment. / Doctor of Philosophy / On average, each of us produces 3 – 4 pounds of solid waste every day. In the U.S., the yearly generation of solid waste is 250 million tons, while the global generation is 1.1 billion tons. The global management cost of solid waste is around 200 billion dollars. About half of U.S. municipal solid waste ends up in landfills, in China, this number is 80%. Among the different municipal solid waste (MSW) management approaches, landfilling is the most common because of its low cost and relatively low maintenance requirements. In a landfill, the combination of precipitation and solid waste degradation produce leachate, a complex wastewater. A ton of municipal solid waste can generate 0.05–0.2 tons of leachate in its lifetime during the process of landfilling. Leachate contains a vast array of pollutants, which can result in major environmental impact and adverse human health risk if not contained and treated appropriately. At present, leachate is mostly treated biologically, without any resource recovery. Among the myriad recoverable resources in landfill leachates, water and ammonia are the most abundant. We applied innovative approaches such as, bioelectrochemical systems, forward osmosis, advanced oxidation to recover resources and remove contaminants from leachate simultaneously. We also incorporated these novel technologies to help each other. For instance, we recovered humic fertilizer from leachate prior to advanced oxidation (i.e., Fenton’s oxidation) that helped the reduction of Fenton’s reagent requirements. The next step of our study could be the pilot scale application of the proposed techniques so that it can be applied in field. The broader impacts of this study include improvements in sustainability and cost efficiency of leachate treatment that can benefit the society.

A novel concept of recovering heat from hot gases using countercurrently flowing vibrofluldized solids (that is, solids levitated solely by mechanical vibration) has been proposed and tested. Based on a theoretical heat transfer model, the heat transfer coefficient between the air and the solids was calculated. A factorial design of experiments showed that a higher heat transfer coefficient was obtained with higher air flow rates and lower solid flow rates. The baffle height had an insignificant affect on the heat transfer. Tests with multiple baffles led to a maximum heat transfer coefficient (143 W/m²-K) when using four baffles. For all tests performed in this work, the solids were not truly vibrofluldized. Instead, they were merely vibro-conveyed (or vibro-shuffled) as a single mass. A new vibrating system will provide the sufficient energy for vibrofluidization, and enhanced heat transfer is expected. This work demonstrated for the first time the solid impeding phenomenon in a fluidized-bed heat exchanger. Specifically, experimental tests showed that if a baffle was lowered past a limiting height at given air and solid flow rates, the increased air velocity past a baffle could prevent the solids from exiting the exchanger. An economic evaluation showed that the vibrofluidized-bed heat-exchanger system would be economically feasible for the production of boiler feedwater using heat recovered from boiler combustion gases. The payback time for the system could be as little as 1.4 years. The convective heat-transfer data from a supernatant gas to a flowing vibrofluidized bed of solids were the first of their kind, and they have led to a better understanding of the new vibrofluidized-bed heat-exchanger system. The successful completion of this project sheds encouraging light onto future heat-recovery operations with such a system. / Master of Science

A novel concept (called “heat tray”) is proposed for heat recovery from hot gases and for heat management in exothermic catalytic reactions, which involves a supernatant gas (S-gas) flowing over a shallow fluidized bed of solids. This thesis presents the results of bench-scale and pilot-scale experimental studies that quantify heat transfer between the S-gas and the shallow fluidized bed. A fractional-factorial design of experiments was performed on two heat-tray systems using three different results showed that fine fluid cracking catalyst (FCC) particles out-performed larger alumina spheres as a fluidized solid. Heat transfer coefficients between the supernatant gas and the shallow fluidized bed approached 440 W/m²-K using FCC. Various S-gas inlet nozzle configurations were studied, with a nozzle height equal to one-half of the static bed height (0.051 m) giving the best results. The study showed that short heat-tray lengths (<0.8 m) are desirable and that S-gas redistributors are needed to compartmentalize the unit. An economic analysis showed that the proposed heat tray would be economically feasible for adaption as a boiler feedwater preheater in a small steam-generation facility, using boiler combustion gases as the S-gas. The payback time for the system would be as short as 1.9 years when used continuously. The heat transfer results from a S-gas to a flowing shallow fluidized bed represent the only data reported thus far, and have led to a better understanding of the new shallow fluidized-bed system for heat-exchange applications. / Master of Science

Magnesium oxide (MgO) is a cost-effective and environmentally sustainable alternative to magnesium chloride (MgCl2) and sodium hydroxide (NaOH) used for sidestream struvite recovery from anaerobically digested supernatant (centrate) through the Pearl® process. MgO is produced from magnesite (MgCO3) calcination, and different calcination conditions can alter the quality and characteristics of the MgO product. It was hypothesized that the insolubility of MgO could provide a "slowly available" form of Mg2+ in the reactor and consequently allow the reactor to be operated beyond design phosphorus (P) reactor loading. MgO has been utilized in other P recovery technologies, e.g. the Phospaq™ Process, but operation and performance of MgO using a full-scale Pearl® 500 fluidized bed reactor was investigated. Performance at rated reactor loading utilizing MgO was initially comparable to baseline conventional MgCl2 reactor operation, ≥50% struvite yield (P recovered/theoretical P recovery) and ≥70% total phosphorus (TP) removal. However, the pilot reactor operated at 2X reactor loading showed comparable results to baseline performance at 1.5X reactor loading. During the full-scale pilot, optimization of the reactor utilizing MgO was limited by the struvite product size that the struvite post-processing equipment could effectively harvest. Additionally, the MgO characteristics due to calcination conditions were hypothesized to affect struvite precipitation kinetics. In struvite precipitation jar testing, MgO products were used to analyze the saturation index, measure precipitation kinetics, and understand the effect that MgO hydration and reactivity had on struvite precipitation. Jar testing showed that initial P removal increased with increasing MgO product reactivity. The most reactive MgO used, Timab AK98, showed 1-40% P removal and substantial decrease in solution saturation index immediately after dosing MgO to centrate. The slower P removal and decrease in saturation index observed with the less reactive material suggests that MgO can provide a "slowly available" Mg2+ reserve throughout the struvite precipitation reaction. / Master of Science / Phosphorus is an essential element for human, plant and animal health. Necessary bodily functions cannot be performed without inputting phosphorus to cell metabolic pathways, such as cell repair and formation of nucleic acids, bone mineral and stored energy. Phosphates are the most common form of phosphorus found in the environment and are a component of many common substances, such as detergents, fertilizers, food and urine. Due to the increasing population and food demand the need for phosphorus-based fertilizers has soared since the 1940s. In 2018, 240 megatons of phosphate rock were mined, and 17 megatons of phosphorus were extracted from mined ore. 15 megatons of the extracted phosphorus were used in fertilizer production. Because of phosphorus loss from the soil and inefficient agro-practices, only 20% of the extracted phosphorus is consumed by humans and animals from food and little is then recycled from our waste systems. There is a major gap in the agricultural phosphorus cycle that is necessary to address with sustainable practices (Oster, M. et al. 2018). Phosphorus can be recovered from wastewater in the form of struvite, which is a mineral that can be utilized a slow-release fertilizer. Conventional methods of phosphorus recovery from wastewater have the potential to be costly. By utilizing an alternative chemical, struvite recovery can be more cost-effective and environmentally sustainable.

Fall related injuries are a major public health concern due to their high associated medical costs and negative impact on quality of life. Obese and older adults are reported to fall more frequently than their normal-weight and young counterparts. To help identify potential mechanisms of these falls the purpose of the research within this dissertation was to investigate the effects of obesity and age on the likelihood of tripping and subsequent balance recovery. Four experimental studies were conducted. The purpose of the first study was to investigate the effects of obesity, age and gender on the likelihood of tripping during level walking. Likelihood of tripping was assessed with median minimum foot clearance (MFC) and MFC interquartile range (IQR). Obesity did not increase the likelihood of tripping suggesting the increased rate of falls among obese adults is not likely due to a greater likelihood of tripping over an unseen obstacle. Additional results suggested females and individuals of shorter stature have an increased likelihood of tripping compared to their male and taller counterparts. The purpose of the second study was two-fold. First, the effects of load carriage and ramp walking on the likelihood of tripping were investigated, followed by investigating the effects of age and obesity on the likelihood of tripping during load carriage and ramp walking. Again, likelihood of tripping was assessed with median MFC and MFC IQR. Load carriage increased the likelihood of tripping during both level and ramp walking and obesity and age increased the likelihood of tripping during selected combinations of load carriage and/or ramp walking. These results suggest that the increased rate of falls during load carriage and the increased rate of falls among obese and older adult workers reported elsewhere may be due in part to an increased likelihood of tripping. The third study proposed a new method for investigating the likelihood of tripping as a function of obstacle height. The proposed method aimed to clear up ambiguous results often encountered when using MFC central tendency and variability to quantify likelihood of tripping. The method used trip probability curves and a statistical bootstrapping technique to compare trip probability at specific obstacle heights between groups of interest. An additional benefit of this method was that it was able to identify effects of factors not identifiable by the commonly used ANOVA analysis using MFC central tendency and variability. The purpose of the fourth study was to investigate the effects of obesity, age and gender on balance recovery following a lab induced trip perturbation. Measures of balance recovery included fall rate, stepping strategy and characteristics, and trunk kinematics. Obese, older, and female adults fell more frequently after tripping and this higher fall rate may help explain the higher fall rates among obese, older and female adults reported elsewhere. Failed recoveries were associated with higher peak trunk angles and angular velocities in addition to the use of a lowering strategy. Obese, older, and female adults had higher peak trunk angles and angular velocities and older adults and females used lowering strategies more often. These alterations in trunk kinematics and stepping strategy may have contributed to the higher fall rate among these individuals. / Ph. D.

Recent literature surrounding the process of recovery from work and work-related demands has included the supervisor as a key variable influencing how and if employees recover from work. Recovery represents the return of personal resources to their pre-work levels and is typically conceptualized as taking place during non-work time (e.g., at night after work, weekends, holidays). It is theorized to take place through four main recovery experiences: psychological detachment from work, relaxation, mastery experiences, and control over leisure time. This study extends the literature surrounding recovery experiences to include subordinate perceptions of supervisor recovery as a potential predictor of subordinate recovery and well-being. Participants (N=252) completed three time-lagged surveys and reported their perceptions of their supervisor’s recovery (Time 1), their own recovery (Time 2), and their feelings of vigor and fatigue (Time 3). Perceived supervisor recovery was empirically distinguishable from supervisor support for recovery and provided incremental validity in predicting subordinate recovery beyond this support perception. These results bolster the conclusion that supervisor recovery can spillover to directly influence subordinate recovery. / M.S. / Recent research has focused on how the supervisor may influence how and if subordinates are able to rest and recover from the demands they face at work. The process of recovery from work is usually thought to take place during time away from work (e.g., at night after work, weekends, holidays) and is thought to occur through four experiences: psychological detachment from work (cutting mental and physical ties with work), relaxation (positive mood and low effort), mastery experiences (building skills or hobbies), and control over leisure time (being able to decide how to spend one’s time). This thesis extends previous work to include subordinate perceptions of how his / her supervisor is recovering from work as a potential predictor of subordinate recovery and recovery related outcomes. Participants (N=252) completed three surveys over the course of four weeks and reported their perceptions of their supervisor’s recovery (Survey 1), their own recovery (Survey 2), and their feelings of vigor and fatigue (Survey 4). Subordinate perceptions of the mastery and control of their supervisor was related to subordinate mastery and control above and beyond existing measures of how the supervisor may influence subordinate recovery. These results suggest that the supervisor may be an important role model in how subordinates recover.

The advent of cluster computing has resulted in a thrust towards providing software mechanisms for reliability on clusters. The prevalent model for such mechanisms is to take a snapshot of the state of an application, called a checkpoint and commit it to stable storage. This checkpoint has sufficient meta-data, so that if the application fails, it can be restarted from the checkpoint. This operation is called a restore. In order to record a process' complete state, both its volatile and persistent state must be checkpointed. Several libraries exist for checkpointing volatile state. Some of these libraries feature incremental checkpointing, where only the changes since the last checkpoint are recorded in the next checkpoint. Such incremental checkpointing is advantageous since otherwise, the time taken for each successive checkpoint becomes larger and larger. Also, when checkpointing is done in increments, we can restore state to any of the previous checkpoints; a vital feature for adaptive applications. This thesis presents a user-level incremental checkpointing library for files: Metamori. This brings the advantages of incremental memory checkpointing to files as well, thereby providing a low-overhead approach to checkpoint persistent state. Thus, the complete state of an application can now be incrementally checkpointed, as compared to earlier approaches where volatile state was checkpointed incrementally but persistent state had no such facilities. / Master of Science

Containers are an alternative to virtual machines rapidly increasing in popularity due to their minimal overhead. To help facilitate their adoption, containers use management systems with central registries to store and distribute container images. However, these registries rely on other, preexisting services to provide load balancing and storage, which limits their scalability. This thesis introduces a new registry design for Docker, the most prevalent container management system. The new design coalesces all the services into a single, highly scalable, registry. By increasing the scalability of the registry, the new design greatly decreases the distribution time for container images. This work also describes a new Docker registry benchmarking tool, the trace player, that uses real Docker registry workload traces to test the performance of new registry designs and setups. / Master of Science