Synchronization of electrically coupled resonate-and-fire neurons

Electrical coupling between neurons is broadly present across brain areas and is typically assumed to synchronize network activity. However, intrinsic properties of the coupled cells can complicate this simple picture. Many cell types with strong electrical coupling have been shown to exhibit resonant properties, and the subthreshold fluctuations arising from resonance are transmitted through electrical synapses in addition to action potentials. Using the theory of weakly coupled oscillators, we explore the effect of both subthreshold and spike-mediated coupling on synchrony in small networks of electrically coupled resonate-and-fire neurons, a hybrid neuron model with linear subthreshold dynamics and discrete post-spike reset. We calculate the phase response curve using an extension of the adjoint method that accounts for the discontinuity in the dynamics. We find that both spikes and resonant subthreshold fluctuations can jointly promote synchronization. The subthreshold contribution is strongest when the voltage exhibits a significant post-spike elevation in voltage, or plateau. Additionally, we show that the geometry of trajectories approaching the spiking threshold causes a "reset-induced shear" effect that can oppose synchrony in the presence of network asymmetry, despite having no effect on the phase-locking of symmetrically coupled pairs

Development of a Two-dimensional Model of a Pneumatic Tire

The pneumatic tire has been studied extensively since its invention in 1888. With the advent of high-powered computers and the use of the finite element method, the understanding of the tire\u27s complex non-linear behavior has grown tremendously. However, one weakness of finite element models is that parameter studies are difficult and time consuming to perform. In contrast, an analytical model can quickly and easily perform extensive parameter studies. To the knowledge of the author, all existing analytical models of the tire make assumptions concerning the tire\u27s behavior and construction that while useful for obtaining some of the first-order characteristics, are limited since they cannot relate tire behavior such as force-deflection to individual tire stiffnesses. As such, an adequate two-dimensional model of a pneumatic tire, including a finite element model, does not exist. Therefore, an analytical, two-dimensional model for a pneumatic tire in static contact with a rigid surface is developed and presented. The case of a non-pneumatic tire can be obtained as a special case. The quasi-static investigation concentrates on finding the relationships between the tire\u27s size and stiffness and its deformation under loading. A total of seven stiffness parameters are accounted for. The belt of the tire is modeled using curved beam theory, developed by Gasmi, et al. (2011), which accounts for bending (EI), shearing (GA), and extensional (EA) deformations. The sidewall of the tire is modeled as a bi-linear spring (KrT, KrC) with pre-tensioning (FP*) in the radial direction and a linear torsional spring (Kθ) in the circumferential direction. Application of virtual work leads to a set of 6th order differential equations for the displacements in the belt that must be solved in three distinct regions. The first region is the region where the radial deformation is greater than the radial deformation of the inflated and unloaded tire. The second region is the region where the radial deformation of the sidewall is less than the inflated position but not in contact with the ground, and the third region is defined to be the region in contact with the ground. The length of the contact patch is represented by the angle enclosed by the edges of contact, and analytical expressions of stress resultants and displacements at the centroids of cross-sections are expressed in terms of this angle. In order to improve the accuracy of the model for large deformations, a special inflation pressure was calculated that allowed the most accurate solution to the linear model to be obtained by minimizing the circumferential force in the region of the largest rotation of the curved beam. This solution was then modified to account for the true inflation pressure. This two-step solution procedure was validated with a geometrically nonlinear finite element model of a non-pneumatic tire. Force vs. deflection and force vs. counter deflection results were compared to experimental data for a pneumatic tire for a range of inflation pressures from zero to four bar. From this, it is concluded that while it is clearly possible to match the data, more work needs to be done to determine the best method for determining parameters that match a real tire. Extensive sensitivity analysis was performed on all the stiffness parameters

Black Curativeness: Understanding Black Voter Selection through an Assessment of Racially-charged Districts

Since the passage of the Voting Rights Act of 1965 most scholarship on Black voter selection explains who Black voters select as opposed to why they select them. This study seeks to deepen understandings of Black voter selection beyond descriptive explanations through an assessment of a racially-charged district. Racially-charged districts can be used as microcosms for understanding political thought and behavior of racial minorities, particularly Black voter selection. These locales, where proven racial inequity propels race and racism as the overarching themes for all political and social concerns, are important in understanding why Black voters show positive affect towards viable Black candidates. Using data from the 2016 University of Missouri-St. Louis Exit Poll, this research provides evidence towards explaining why a candidate’s race is a prominent factor in vote choice for Black voters. The study concludes a substantial segment of the Black voting demographic view the election of Black officials as paramount and remedial to enduring institutional discrimination on the basis of race—a notion of Black curativeness

The aerodynamic response of airborne discs

A study has been conducted to characterize the flow over a free-flying disc. In this study, three types of discs are analyzed in a series of stationary experiments, and a single disc is analyzed in a spinning experiment. Two dimensionless parameters dominate the experiments, the Reynolds number and the tip speed ratio. The first experiment measured the lift and drag at varying angles of attack on a stationary disc. The second stationary experiment was a unique measurement of the center of lift of a disc as a function of velocity. The third stationary experiment was a tuft test to describe the boundary layer, done at different velocities and angles of attack. The spinning disc experiment utilized smoke to visualize the flow around the disc and ascertain the effects of spin on vorticity and boundary layer separation. Results showed that the center of lift was behind the geometric center at low velocity and moved rapidly forward with increasing velocity. Tuft and smoke tests showed that the boundary layer was attached across the entire surface with strong vortices shed from the sides and from the rear of the disc. The flow was primarily affected by the disc\u27s leading edge with secondary effects from the domed contour

Repercussive Discrimination: Racial Discrimination as an Explanation of Prevalent Homophobia Among Racial Minorities

Generally, attitudes in the United States towards lesbian, gay, bisexual, transgender, and intersex (LGBTI) persons have become more favorable in recent years. Obviously, examining the politics of LGBTI persons and attitudes towards them is important considering that this demographic may account for 10% of the U.S. population; but a more inconspicuous reason it that examinations provide insight into the political landscape of how political minorities address various issues and interests. However, in studying public opinion towards gays and lesbians it is discovered that racial minorities, particularly African-Americans, generally possess negative attitudes to LGBTI persons and possess higher percentages of homophobic persons when compared to Whites. Some may assert the notion of racial minorities being more homophobic goes against logical arguments of empathy, considering that racial minorities have historically and, to some extent, currently face discrimination and marginalization. This dissertation is an examination of the salient homophobia among racial minorities in light of national attitudes that are becoming more favorable towards the gay and lesbian minority. The explanations in literature are too often reliant on the antiquated narratives of religiosity, particularly the salience of the Black Church. This study asserts merit for a new theory, termed repercussive discrimination, which may be equally as impactful in understanding negative attitudes towards LGBTI persons. Based on the principles of transference, this theory asserts that an experience with racial discrimination is casual in homophobic attitudes for racial minorities. This study arrives at this determination by using a mixed methods approach to determine assess the significance of variables in determining a racial minority’s propensity towards homophobia measured in different ways. By performing quantitative analyses of statistical data from 2000-2014 from the American National Election Study (ANES) and the General Social Survey (GSS) and qualitative analysis of expert interviews, public records, and audiovisual materials, this dissertation finds: (1) no singular variable can explain homophobia for racial minorities; and (2) there is legitimacy for theories, which prompt new approaches to understanding these attitudes, such as repercussive discrimination

Analysis of Traffic Conflicts in a Mixed-Airspace Evaluation of Airborne Separation Assurance

A pair of human-in-the-loop simulation evaluations of a distributed air/ground separation assurance system have been conducted to investigate the function allocation between humans and automation systems as well as ground-based and airborne agents in the Next Generation Air Transportation System and beyond. This paper focuses on an analysis of certain critical conflicts observed between self-separating aircraft and ground-managed traffic in the same airspace. The principal cause of each conflict is identified and potential mitigations are discussed, such as: the sharing of trajectory intent information between the ground and the air; more cautious trajectory planning by the self-separating aircraft; and more equitable rules-of-the-road between the self-separating aircraft and ground-managed aircraft. This analysis will inform the ongoing design of an airborne separation assurance automation tool