An unsteady Reynolds Averaged Navier-Stokes (URANS) based turbulence model, the Spalart-Allmaras (SA) model, was used to investigate the flow pulsation phenomenon in compound rectangular channels for isothermal flows. The computational fluid dynamics (CFD) commercial package ANSYS CFX-11.0 was used for the simulations. The studied geometry was composed of two rectangular subchannels connected by a gap, on which experiments were conducted by Meyer and Rehme [34] and were used for the validation of the numerical results. Two case studies were selected to study the effect of the advection scheme. The results using the first order upwind advection scheme had clear symmetry and periodicity. The frequency of the flow pulsations was underpredicted by almost a factor of two. Due to the inevitable numerical diffusion of the first order upwind scheme, it was more appropriate to use a second order accurate in space advection scheme for comparison with the experiments. The span-wise velocity contours and the velocity vector plots at planes parallel to the bulk flow, together with the time traces of the velocity components at selected monitor points showed the expected cross-flow mixing between the subchannels through the gap. Although the SA model does not solve directly for the turbulence kinetic energy, a kinetic energy associated with the unsteady solutions of the momentum equations was evaluated and qualitatively compared with the experimental turbulence kinetic energy. The calculated kinetic energy followed the trends of the experimental turbulence kinetic energy at the gap area, predicting two peaks at the edges of the gap. The dynamics of the gap pulsations were quantitatively described through temporal auto-correlation and auto-power spectral density functions and the numerical predictions were in agreement with the experiments. Studies on the effect of the Reynolds number and the computational length of the domain were also carried out. The numerical results reproduced the relationship between the Reynolds number and the frequency of the auto-power spectral density functions. The impact of the channel length was tested by simulating a longer channel. It was found that the channel length did not significantly affect the predictions. Simulations were also performed using the (kappa) -(epsilon) model. While flow pulsations were predicted with this model, the frequency of the pulsation was in poor agreement with the experimentally measured value. / Thesis / Master of Applied Science (MASc)

The functionality of a novel 3-dimensional betavoltaic battery design will be investigated to improve conversion efficiency over existing planar devices. A beta-emitting isotope of nickel, Ni-63, is embedded in the volume of empty space between self-assisted p-i-n junction gallium phosphide nanowires to improve the beta capture efficiency. Parameters such as nanowire pitch, diameter, and height will influence the efficiency and were investigated thoroughly. Material selection was performed based on the following considerations. Gallium phosphide is chosen to achieve a high open circuit voltage under beta exposure. Ni-63 has an optimal beta energy spectrum for a nanowire device and a half-life of 101 years for long term application. The majority of the work focused on the development of the fabrication process, particularly the radioactive source deposition. The method used for embedding the source was a citrate-based sol-gel which was spun onto the sample. This method was modified for this nanowire application and specific challenges to the process are outlined. Furthermore, the obstacles of working with radioactive materials will be discussed. The first nanowire-based betavoltaic device is reported to produce beta-generated current and achieved a beta conversion efficiency of 0.03%. Investigation of the junction was performed to provide future improvements to the efficiency. Additionally, simulated IV curves for a non-active sample exhibited a possible conversion efficiency of 1.92%. / Thesis / Master of Applied Science (MASc)

Background: Tuberculosis (TB) is the number one infectious disease killer in the world. TB is both preventable, and curable. Since 1997, the World Health Organization’s (WHO) Global TB (GTB) Programme has released evidence-informed publications to guide member states. In their EndTB strategy, the WHO set a mandate to eradicate TB by 2035, in part by intensifying TB research and innovation. As an effort towards this goal, this project applies evidence mapping methodologies to published WHO TB recommendations, in an innovative process called “recommendation mapping” (RM). Objectives: The prime objective of RM is to allow guideline developers and key stakeholders to identify gaps and clusters of recommendations across publications, serve as an instrumental tool in the sequence of guideline development (from intelligent priority setting, to the assembly of final recommendations) and increase the accessibility of key guideline components. The secondary objective of this work is to poise guideline components for live update and refinement in a rapidly learning health system. Methods: In this mixed methods study, a methodological framework for mapping guideline components is proposed, with both a quantitative and narrative assessment of raw data and final map outputs. A qualitative analysis from the perspective of key stakeholders, policy-makers, researchers and WHO-GTB liaisons working in guideline development is also included. For the methodological piece, all publications containing WHO TB recommendations were eligible for the mapping exercise. Each recommendation was extracted according to all subdomains of their PICO backbone. Subsections of recommendations are coded using existing ontologies (SNOMED-CT, ATC, ICD-11). A centralized database containing extracted and coded recommendations was then presented in an online and interactive schematic. For the qualitative assessment of palatability of this approach within the organization, semi-structured interviews and a survey was delivered to eligible participants at two Guideline Development Group meetings for WHO tuberculosis treatment and screening guidelines. Results: The notable result of this work is the development, refinement and application of recommendation mapping methodologies. 20 WHO-GTB guidelines underwent an application of the novel recommendation methodologies proposed in this thesis to create an interactive map, and a searchable database. In-depth interviews and survey results with 21 participants (WHO GTB staff, WHO TB- guideline development group members and technical experts) pointed to concerns in the current accessibility and organization of WHO-GTB guidelines. Conclusions: Recommendation mapping may have utility in charting the terrain of recommendations, inform priority setting, and provide a scaffold for the future transition to living guidelines. / Thesis / Master of Public Health (MPH) / The World Health Organization (WHO) issues guidelines to help clinicians, policy-makers, and researchers make informed decisions in their work. Guidelines contain recommendations that can be thought of as bottom-line answers to the questions we ask the scientific literature (based on the evidence available to us today). The WHO’s Tuberculosis (TB) Department is partaking in a novel digital reorganization of their guideline recommendations using the evidence-mapping methods proposed in this thesis. This thesis uses the principles of evidence mapping to create recommendation maps that, like any map, chart the landscape in a given domain (in this case, TB recommendations). The recommendation map will help guide the WHO in setting priorities for future research and guideline development.

Gap crossing is a regular locomotor activity for arboreal animals. The distance between branches likely plays a role in determining whether an animal is capable of crossing a given gap, and what locomotor behavior it uses to do so. Yet, despite the importance of gap distance as a physical parameter influencing gap crossing behavior, the precise relationships between gap distance and movement kinematics have been explored in only a very small number of species. One particularly interesting group of arboreal inhabitants are the flying snakes (Chrysopelea). This species is able to use a dynamic "J-loop" movement to launch its glides, but it is not known whether it is also capable of using such jumps to cross smaller gaps between tree branches. This dissertation addresses this knowledge gap, and investigates the influence of gap distance on crossing behavior and kinematics in three closely-related species of snake: Chrysopelea paradisi, a species of flying snake, and two species from the sister genus, Dendrelaphis, neither of which can glide. Chapter 2 is a literature review of the biomechanics of gap crossing, specifically focusing on the role played by gap distance, and establishes the context for the rest of the work. Chapter 3 presents a detailed study of how increasing gap size influences the behavior and kinematics of gap crossing in C. paradisi, showing that this species uses increasingly dynamic movements to cross gaps of increasing size. Chapter 4 explores the same relationships between gap size and kinematics in D. punctulatus and D. calligastra, revealing remarkable similarities between the three species, suggesting the possibility that dynamic gap crossing may have evolved prior to gliding in this clade. Finally, chapter 5 addresses the role played by gap distance in limiting the non-dynamic, cantilever movements used by these species to cross small gaps, comparing observed stopping distances to those predicted by various torque-related limitations. / Doctor of Philosophy / To successfully cross a gap, an animal must be able to reach or jump from one side to the other. Animals who live in trees must do this quite frequently, as they live among the branches and there are often not connected paths from one place to another. But we don't know very much about how the distance between two structures (the "gap distance") affects the ways an animal moves between them. In this dissertation, I explore how gap distance changes the way a few special species of snakes cross a gap. The species I am studying are special because one species, the paradise tree snake, can glide. Because this 'flying' snake launches its glides by doing a big jump, it is possible that the snake can also jump between tree branches, but this question has never been examined before. We also don't know how the ability to do big jumps evolved, so I studied how distance affects the way two very closely related species of snake, the common tree snake and the northern tree snake, cross gaps. By looking at all of these species, we can understand more about what kinds of behavior are specific to the flying snakes, and which are present in related species. Finally, I also explore how gap distance limits the way the snakes cross gaps when they are not jumping. When the snakes do not jump, they have to hold themselves out straight off the end of a branch. This requires a lot of muscular effort, which means they can't go as far. The fact that the non-jumping behavior is distance-limited might help explain why the snakes need to jump. Altogether, the projects in this study help us understand how gap distance influences what behavior an animal chooses to cross the gap, and increases our knowledge of how flying snakes and their relatives cross gaps in particular.

This dissertation examines aspects of both the consumer (the "give") and the server (the "take") sides of restaurant tipping. On the consumer side, I address both why, and how much, people tip in restaurants. I also examine a policy issue related to the recent Supreme Court decision in United States v. Fior d'Italia. These issues are addressed via a combination of theoretical, empirical, and experimental analysis. On the server side, I use survey data collected from several restaurants to address the issue of labor market discrimination based on beauty. Specifically, do more attractive servers earn higher tips than less attractive servers? I argue that a tipping data set offers several advantages over data sets used in previous studies of the beauty wage gap. This dissertation was funded by a National Science Foundation Dissertation Enhancement Grant (NSF #427347). / Ph. D.

In a form of controlled electromagnetic suspension, a permanent magnetic is levitated by a magnetic field; the field is produced by electrical currents passing through coils. These currents are the control input. In a Large-Gap system the coils are at some distance from the suspended body; in general, there is no closed form expression relating the currents to the flux at the point of the suspended body. Thus, in the general case, it is not possible to establish control-theoretic results for this kind of Large-Gap suspension system. It is shown, however, that if the coil placement configuration exhibits a particular cylindrically symmetric structure, expressions can be found relating the coil positions to the flux. These expressions are used to show the existence of a unique equilibrium point and controllability, in five dimensions of control, for a generic form of Large-Gap system. The results are shown to remain true if the suspended body is rotated about a particular axis. Closed form expressions are found for the currents required to suspend the body at these variable orientations. An inequality between difference classes of experimental inputs is shown to be a necessary condition for suspension of the body. It is demonstrated that the addition of coils to the system cannot lead to six dimensions of controllability. Let the system be given by the standard control equation 𝑥̇=𝐴𝑥+𝐵𝑢 Closed form expressions are found for the eigenvalues of 𝐴. In the course of proving that some coil placement restrictions may be relaxed, 𝐵 is shown to be related to the Vandermonde matrix. / Ph. D.

Studies suggest a relationship exists between school climate and student achievement (Hoy & Woolfolk, 1993; Smith, 2005; Warren, 2007). This study investigated the relationship between school climate and student achievement in elementary schools located in a school division in Virginia. School climate is defined operationally as the perceptions of stakeholders, students, parents and educators in regard to instructional programming, interpersonal relationships, communication/collaboration, safety/discipline, and physical environment. The factors that shape school climate and the perceptions of students, parents, and educators in regard to school climate were also investigated. The population for this study was 55 elementary schools in the selected school division. The study used hierarchical clustering to cluster the schools into four clusters. The clusters were analyzed to determine if a relationship existed between school climate and student achievement. Regression analysis was completed on school climate and student achievement data from each school. The purpose of this analysis was to investigate the relationship between the factors of school climate and student achievement. Of additional interest was the relationship between student achievement and the perspective of stakeholders in regard to school climate. This study used data from the 2007-2008 fifth grade Virginia Standards of Learning (SOL) tests in reading and math to measure student achievement. Data collected from the school division's 2008 Annual School Climate Survey was used to measured school climate In the content areas of reading and math lower pass percentages on the Virginia SOL tests related to lower agree percentages in response to the School Climate Survey. Conversely, in the content areas of reading and math higher pass percentages on the Virginia SOL tests related to higher agree percentages in response to the School Climate Survey. Based on these findings schools that have a negative school climate as perceived by its stakeholders can expect to have lower student achievement scores, whereas, schools with a positive school climate as perceived by its stakeholders can expect to have higher student achievement scores. The analysis of data representative of school climate and student achievement found a relationship exists between school climate and student achievement. / Ph. D.

With the decrease in availability of non-renewable energy sources coupled with the increase in the amount of energy required for the operation of personal electronic devices there has been an increased focus on developing systems that take advantage of renewable energy sources. Renewal energy sources such as photovoltaic (PV) panels have become more popular due to recent developments in PV panel manufacturing that decreases material costs and improves energy harvesting efficiency. Since PV sources are DC sources power conversion stages have to be used in order to interface this power to the existing electrical utility system. The structure of large scale PV systems usually consists of several PV panels connected in series to achieve a high input source voltage that can be fed into a high power centralized DC-AC inverter. The drawback to this approach is that when the PV panels are subjected to less than ideal conditions. If a single PV panel is subjected to drastically less solar irradiation during cloud conditions, then its output power will drop dramatically. Since this panel is series connected with the other PV panels, their current output is also dragged low decreasing the power output of the system. Algorithms that have the power converter operate at different input conditions allow the system to operate at a maximum power point (MPP), however this only allows the system to operate at a higher power point and not the true MPP. To get around this limitation a new PV system implementation was created by giving each panel its own DC-AC power conversion system. This configuration gives each panel the ability to operate at its own MPP increasing the total system energy harvest. Another advantage of the single panel DC-AC microinverter power conversion stage is that the outputs are parallel connected to the utility grid easily allowing the ability to expand the system without having to shut down the entire system. The most prevalent implementation of the microinverter consists of a single power converter that uses the PV low voltage DC and outputs high voltage AC. In order to ensure that the double line AC ripple does not propagate to the PV panel a large bank of electrolytic capacitors are used to buffer the ripple. There is concern that the electrolytic capacitor will degrade over time and affect the system efficiency. To get around having to use electrolytic capacitors a two stage microinverter has been proposed. The two stage microinverter consists of a DC-DC converter that steps up the low DC voltage of the PV panel to high voltage DC and the second stage is a DC-AC inverter that takes the high voltage DC and converts it to high voltage AC. There is a capacitor that connects the two power converter stages called the DC link capacitor which can buffer the double line energy ripple without using electrolytic capacitors. This thesis focuses on the review of several DC-AC inverter topologies suitable for use in PV microinverter systems. Operation capabilities such as common mode noise and efficiency are compared. The main focus of the review is to determine the optimal DC-AC inverter using the performance metrics of cost, efficiency and common mode performance. A 250 W prototype is built for each inverter topology to verify its performance and operation. / Master of Science

Sudden cardiac death occurs due to aberrations in the multifactorial process that is cardiac conduction. Conduction velocity (CV) and its modulation by several determinants, like cellular excitability, tissue structure and electrical coupling by gap junctions (GJ), have been extensively studied. However, there are several discrepancies in cardiac electrophysiology research that have extended over decades, suggesting elements that are still not completely understood about this complex phenomenon. This dissertation will focus on one such mechanism, ephaptic coupling (EpC). The purpose of this work is twofold, 1) to identify ionic determinants of EpC, and its interactions with gap junctional coupling (GJC) and, 2) to investigate the possible role of serum ion modulation in cardiac arrhythmia therapy. First, the effects of altering extracellular ion concentration – sodium, potassium and calcium at varying GJ protein expression were studied. Briefly, reducing sodium was related to CV slowing under conditions of reduced EpC (wide intercalated disc nanodomains – perinexi) and GJC (reduced GJ protein – Connexin43). On the other hand, increasing potassium slowed CV in hearts with wide perinexi independent of GJC. Elevating calcium, reduced perinexal width and was associated with fast CV during physiologic sodium concentration. However, under conditions associated with disease, like hyponatremia, elevating calcium still reduced perinexal width but slowed CV. These findings are the first to suggest that ionic modulators of EpC could modulate CV during health and disease. Next, the potential of perfusate ion modulation in cardiac arrhythmia therapy was investigated. Briefly, in a model of myocardial inflammation, TNFα, a pro-inflammatory cytokine, slowed CV relative to control conditions and this was associated with widening of the perinexus (reduced EpC). Increasing extracellular calcium restored CV to control values by improving not only EpC but also GJC. Finally, in a model of metabolic ischemia in the heart, CV response due to solutions with varying sodium and calcium concentrations were tested. The solutions that were associated with wider perinexi and elevated sodium performed best during ischemia by attenuating CV slowing, reducing arrhythmias and increasing time to asystole. Taken together, these findings provide evidence for the possibility of ionic determinants of EpC in cardiac arrhythmia therapy. / Ph. D.

Connexins are transmembrane proteins that form hemichannels allowing the exchange of molecules between the extracellular space and the cell interior. Two hemichannels from adjacent cells dock and form a continuous gap junction pore, thereby permitting direct intercellular communication. Connexin 36 (Cx36), expressed primarily in neurons, is involved in the synchronous activity of neurons and may play a role in aberrant synchronous firing, as seen in seizures. To understand the reciprocal interactions between Cx36 and seizure-like neural activity, we examined three questions: a) does Cx36 deficiency affect seizure susceptibility, b) does seizure-like activity affect Cx36 expression patterns, and c) does acute blockade of Cx36 conductance increase seizure susceptibility. We utilize the zebrafish pentylenetetrazol (PTZ; a GABA(A) receptor antagonist) induced seizure model, taking advantage of the compact size and optical translucency of the larval zebrafish brain to assess how PTZ affects brain-wide neuronal activity and Cx36 protein expression. We exposed wild-type and genetic Cx36-deficient (cx35.5-/-) zebrafish larvae to PTZ and subsequently mapped neuronal activity across the whole brain, using phosphorylated extracellular-signal-regulated kinase (pERK) as a proxy for neuronal activity. We found that cx35.5-/- fish exhibited region-specific susceptibility and resistance to PTZ-induced hyperactivity compared to wild-type controls, suggesting that genetic Cx36 deficiency may affect seizure susceptibility in a region-specific manner. Regions that showed increased PTZ sensitivity include the dorsal telencephalon, which is implicated in human epilepsy, and the lateral hypothalamus, which has been underexplored. We also found that PTZ-induced neuronal hyperactivity resulted in a rapid reduction of Cx36 protein levels within. 30 minutes and one-hour exposure to 20 mM PTZ significantly reduced the expression of Cx36. This Cx36 reduction persists after one-hour of recovery but recovered after 3-6 hours. This acute downregulation of Cx36 by PTZ is likely maladaptive, as acute pharmacological blockade of Cx36 by mefloquine results in increased susceptibility to PTZ-induced neuronal hyperactivity. Together, these results demonstrate a reciprocal relationship between Cx36 and seizure-associated neuronal hyperactivity: Cx36 deficiency contributes region-specific susceptibility to neuronal hyperactivity, while neuronal hyperactivity-induced downregulation of Cx36 may increase the risk of future epileptic events. / Doctor of Philosophy / Within the brain, cells (neurons) communicate with each other to pass along information. This communication is important for normal functions of the brain such as learning and memory, muscle movement, etc. Epilepsy is a disease of the brain that is caused by rapid over synchronized communication between cells. This leads to seizures which can include convulsions, loss of attention, and much more. Currently, 30% of patients suffering from epilepsy do not have a treatment option that works for them, it is, therefore, imperative to investigate new targets for treatment in this disease. Connexin36 is a protein in the brain that directly connects cells so they can pass information quickly between them. Connexin36, therefore, might make a good target for treatment. Previous work has aimed to understand this relationship but has been limited in their ability to look at the entire brain at any one time. The goal of this study was to understand the relationship between connexin 36 and brain hyperactivity across the whole brain simultaneously. To understand this relationship, we first determined what happened to brain activity if the protein was missing entirely after exposure to a seizure causing drug. We were asking: How does connexin 36 affect hyperactivity. We found that different regions of the brain responded differently without the connexin 36 protein. This suggests that one size does not fit all, and one must look at the whole brain to understand the effects of the connexin 36 protein. Next, we asked a similar question, but in the opposite direction, how does hyperactivity affect connexin 36? We found, in the short-term, hyperactivity reduced the amount of connexin 36 present in certain regions of the brain. This continued until 3 hours following exposure to the seizure causing drug Pentylenetetrazol (PTZ). Lastly, to determine if this short-term reduction in connexin 36 meant that an individual was more likely to experience hyperactivity. To do this, we used a connexin 36 blocking drug, then introduced the seizure causing drug at different concentrations. We found, at all concentrations, the connexin 36 blocking drug caused significant changes in neuronal activity, depending on the brain regions. Overall, our results showed that connexin 36 plays an important role in hyperactivity and that a short-term reduction in connexin 36 is detrimental, and may contribute to an increase in the possibility of subsequent hyperactivity.