Senior Recital: Stephen P. Orland, Bass Trombone

Kemp Recital Hall Sunday Afternoon November 17, 1991 12:30p.m

Bremsstrahlung from a microscopic model of relativistic heavy ion collisions

We compute bremsstrahlung arising from the acceleration of individual charged baryons and mesons during the time evolution of high-energy Au+Au collisions at the Relativistic Heavy Ion Collider using a microscopic transport model. We elucidate the connection between bremsstrahlung and charge stop- ping by colliding artificial pure proton on pure neutron nuclei. From the inten- sity of low energy bremsstrahlung, the time scale and the degree of stopping could be accurately extracted without measuring any hadronic observables. PACS: 25.75.-q, 13.85.Q

Non-LTI Antenna Design and Modeling Techniques

Nearly all contemporary antenna systems are Linear Time-Invariant (LTI) devices, and allow for assumptions of frequency independence and reciprocity, but are governed by strict bounds on their performance. Recently, nonlinear and time-varying (non-LTI) antennas have become a common path of research in an attempt to break the LTI assumption and improve antenna performance beyond these limits, but lack a general modeling technique to develop fundamental equations for antenna design. The adaptability of the established method of moments (MoM) allows for a complete model of virtually any structure. Conversely, the conversion matrix method allows the expansion of circuit and network parameters to model time-varying structures. The combination of the two methods allows for a generalized model of a time-varying antenna while granting insight into their design. In a similar way, MoM can be combined with the harmonic balance method and allow for the accurate simulation of nonlinear components and pumped nonlinearities on antennas of arbitrary structure. These aspects of MoM, conversion matrices, and harmonic balance are leveraged in this work to provide a better understanding of non-LTI antennas and develop several models for achieving better performance or different capabilities

Investigation of a Frequency and Pattern Reconfigurable Slot Array Utilizing Ring Resonator End Loads

Fixed-bandwidth wireless systems are forced to operate in preallocated blocks of frequencies, often wasting valuable spectrum. Whereas, systems with reconfigurable antennas that can tune resonant frequency, polarization, or pattern allow for versatile systems and efficient spectrum use. Reconfigurable antennas have largely been designed using microstrip transmission line structures since they can be easily printed on a dielectric substrate, making the antenna compact, inexpensive to fabricate, and simple to integrate active components in a series configuration. Slotline is similarly easy to fabricate and has been shown to have some advantages over microstrip in applications such as when active components in a shunt configuration are desired. However, not many reconfigurable antenna architectures have been developed in slotline. Additionally, while frequency- and polarization-agile antennas have been reported by many researchers, antennas with both frequency and pattern reconfiguration capabilities are significantly rare. In this thesis, a closed-form analytical solution for a Yagi-Uda array of loaded slot antennas will be presented. This analysis first evaluates each slot antenna using an established transmission line model then calculates the coupling between the elements using the relative induced power on each antenna. Network parameters are then utilized to model the effects the slot antennas have on each other. The Induced EMF method uses the power incident on one antenna due to another to find the mutual impedance between them - allowing the presented method to be generalizable to any Yagi-Uda array of elements where the radiation pattern is known. The network parameters will be shown to provide an array factor for the Yagi-Uda array - predicting the radiative and directive properties of the array in a closed-form analysis. The analysis method will also be shown to predict the input impedance of the driven element of the array, including the impact of mutual coupling from the parasitic elements, across frequency and for arbitrary array spacings - a result that has not been available with previous analysis methods

A Month in the Life of Groupon

Groupon has become the latest Internet sensation, providing daily deals to customers in the form of discount offers for restaurants, ticketed events, appliances, services, and other items. We undertake a study of the economics of daily deals on the web, based on a dataset we compiled by monitoring Groupon over several weeks. We use our dataset to characterize Groupon deal purchases, and to glean insights about Groupon's operational strategy. Our focus is on purchase incentives. For the primary purchase incentive, price, our regression model indicates that demand for coupons is relatively inelastic, allowing room for price-based revenue optimization. More interestingly, mining our dataset, we find evidence that Groupon customers are sensitive to other, "soft", incentives, e.g., deal scheduling and duration, deal featuring, and limited inventory. Our analysis points to the importance of considering incentives other than price in optimizing deal sites and similar systems.Comment: 6 page

ICAM: Interpretable Classification via Disentangled Representations and Feature Attribution Mapping

Feature attribution (FA), or the assignment of class-relevance to different locations in an image, is important for many classification problems but is particularly crucial within the neuroscience domain, where accurate mechanistic models of behaviours, or disease, require knowledge of all features discriminative of a trait. At the same time, predicting class relevance from brain images is challenging as phenotypes are typically heterogeneous, and changes occur against a background of significant natural variation. Here, we present a novel framework for creating class specific FA maps through image-to-image translation. We propose the use of a VAE-GAN to explicitly disentangle class relevance from background features for improved interpretability properties, which results in meaningful FA maps. We validate our method on 2D and 3D brain image datasets of dementia (ADNI dataset), ageing (UK Biobank), and (simulated) lesion detection. We show that FA maps generated by our method outperform baseline FA methods when validated against ground truth. More significantly, our approach is the first to use latent space sampling to support exploration of phenotype variation. Our code will be available online at https://github.com/CherBass/ICAM.Comment: Submitted to NeurIPS 2020: Neural Information Processing Systems. Keywords: interpretable, classification, feature attribution, domain translation, variational autoencoder, generative adversarial network, neuroimagin

A Minimax Network Flow Model for Characterizing the Impact of Slot Restrictions

This paper proposes a model for evaluating long-term measures to reduce congestion at airports in the National Airspace System (NAS). This model is constructed with the goal of assessing the global impacts of congestion management strategies, specifically slot restrictions. We develop the Minimax Node Throughput Problem (MINNTHRU), a multicommodity network flow model that provides insight into air traffic patterns when one minimizes the worst-case operation across all airports in a given network. MINNTHRU is thus formulated as a model where congestion arises from network topology. It reflects not market-driven airline objectives, but those of a regulatory authority seeking a distribution of air traffic beneficial to all airports, in response to congestion management measures. After discussing an algorithm for solving MINNTHRU for moderate-sized (30 nodes) and larger networks, we use this model to study the impacts of slot restrictions on the operation of an entire hub-spoke airport network. For both a small example network and a medium-sized network based on 30 airports in the NAS, we use MINNTHRU to demonstrate that increasing the severity of slot restrictions increases the traffic around unconstrained hub airports as well as the worst-case level of operation over all airports

Perspectives and Experiences of Participation by Individuals with Disabilities: An Evidence-Based Practice Project

This Evidence-Based Practice (EBP) project considered the following question: How do individuals with disabilities describe their perspectives on and experiences with participation