Learning Efficiency: Is it Generalizable? Is it Durable?

From the Washington University Senior Honors Thesis Abstracts (WUSHTA), Spring 2018. Published by the Office of Undergraduate Research. Joy Zalis Kiefer, Director of Undergraduate Research and Associate Dean in the College of Arts & Sciences; Lindsey Paunovich, Editor; Helen Human, Programs Manager and Assistant Dean in the College of Arts and Sciences Mentor: Kathleen McDermott, Elizabeth Schechter, and Christopher Zer

Multiple populations in globular clusters: the distinct kinematic imprints of different formation scenarios

Several scenarios have been proposed to explain the presence of multiple stellar populations in globular clusters. Many of them invoke multiple generations of stars to explain the observed chemical abundance anomalies, but it has also been suggested that self-enrichment could occur via accretion of ejecta from massive stars onto the circumstellar disc of low-mass pre-main sequence stars. These scenarios imply different initial conditions for the kinematics of the various stellar populations. Given some net angular momentum initially, models for which a second generation forms from gas that collects in a cooling flow into the core of the cluster predict an initially larger rotational amplitude for the polluted stars compared to the pristine stars. This is opposite to what is expected from the accretion model, where the polluted stars are the ones crossing the core and are on preferentially radial (low-angular momentum) orbits, such that their rotational amplitude is lower. Here we present the results of a suite of $N$-body simulations with initial conditions chosen to capture the distinct kinematic properties of these pollution scenarios. We show that initial differences in the kinematics of polluted and pristine stars can survive to the present epoch in the outer parts of a large fraction of Galactic globular clusters. The differential rotation of pristine and polluted stars is identified as a unique kinematic signature that could allow us to distinguish between various scenarios, while other kinematic imprints are generally very similar from one scenario to the other.Comment: 22 pages, 16 figures + appendix. Accepted for publication in MNRA

Robust sound event detection in bioacoustic sensor networks

Bioacoustic sensors, sometimes known as autonomous recording units (ARUs), can record sounds of wildlife over long periods of time in scalable and minimally invasive ways. Deriving per-species abundance estimates from these sensors requires detection, classification, and quantification of animal vocalizations as individual acoustic events. Yet, variability in ambient noise, both over time and across sensors, hinders the reliability of current automated systems for sound event detection (SED), such as convolutional neural networks (CNN) in the time-frequency domain. In this article, we develop, benchmark, and combine several machine listening techniques to improve the generalizability of SED models across heterogeneous acoustic environments. As a case study, we consider the problem of detecting avian flight calls from a ten-hour recording of nocturnal bird migration, recorded by a network of six ARUs in the presence of heterogeneous background noise. Starting from a CNN yielding state-of-the-art accuracy on this task, we introduce two noise adaptation techniques, respectively integrating short-term (60 milliseconds) and long-term (30 minutes) context. First, we apply per-channel energy normalization (PCEN) in the time-frequency domain, which applies short-term automatic gain control to every subband in the mel-frequency spectrogram. Secondly, we replace the last dense layer in the network by a context-adaptive neural network (CA-NN) layer. Combining them yields state-of-the-art results that are unmatched by artificial data augmentation alone. We release a pre-trained version of our best performing system under the name of BirdVoxDetect, a ready-to-use detector of avian flight calls in field recordings.Comment: 32 pages, in English. Submitted to PLOS ONE journal in February 2019; revised August 2019; published October 201

Smart Solutions: Smart Grid Demokit

Treball desenvolupat dins el marc del programa 'European Project Semester'.The purpose of this report is to justify the design choices of the smart grid demo kit. Something had to be designed to make a smart grid clear for people who have little knowledge about smart grids. The product had to be appealing and clear for people to understand. And eventually should be usable, for example, on an information market. The first part of the research consisted of looking how to shape the whole system. How the 'tiles' had to look to be interactive for users and what they should feature. One part of this was doing research to get to know more about the already existing knowledge amount users. Another research investigated what appeals the most to the users. After this, a concept was created in compliance with the group and the client. The concept consists of hexagonal tiles, each with a different function: houses, solar panels, wind turbines, factories and energy storages. These tiles are all different parts of a smart grid. When combining these tiles, it can be made clear to users how smart grids work. The tiles are fabricated using a combination of 3D printing and laser cutting. The tiles have laser cut symbols on top of them to show what part of the smart grid they are. Digital LED strips are on top of the tiles to show the direction of the energy flow, and the colors indicate if the tile is producing or consuming power from the grid. The tiles are connected to each other by the so called “grid blocks”. These blocks make up the central power grid and are also lighting up by LED strips. Each tile is equipped with a microcontroller which controls the LED strips and makes it possible for the different tiles to “talk” with each other. Using this, the central tile knows which tiles are connected to the system. The central tile controls all tiles and runs the simulation of the smart grid. For further development of the project, it can be investigated how to control and adjust the system from an external system, for example by a tablet. The final product consists of five tiles connected by seven grid blocks which show how a smart grid works

Variational Barycentric Coordinates

We propose a variational technique to optimize for generalized barycentric coordinates that offers additional control compared to existing models. Prior work represents barycentric coordinates using meshes or closed-form formulae, in practice limiting the choice of objective function. In contrast, we directly parameterize the continuous function that maps any coordinate in a polytope's interior to its barycentric coordinates using a neural field. This formulation is enabled by our theoretical characterization of barycentric coordinates, which allows us to construct neural fields that parameterize the entire function class of valid coordinates. We demonstrate the flexibility of our model using a variety of objective functions, including multiple smoothness and deformation-aware energies; as a side contribution, we also present mathematically-justified means of measuring and minimizing objectives like total variation on discontinuous neural fields. We offer a practical acceleration strategy, present a thorough validation of our algorithm, and demonstrate several applications.Comment: https://anadodik.github.io

Value versus glamour investing : a South African case

Evidence from international and local studies indicates that the value investment style consistently earns returns above those of the growth investment style. The same principle seems to apply, in an international context, when using the glamour investment style, which is a sub-style of growth, as a comparative to value investing. This study aims to prove which style, value or glamour, outperforms the other thereby confirming or denying the presence of an international phenomenon in a South African context. This study replicates a two-variable method that was pioneered in the United States, to divide stocks into value and glamour portfolio’s each year. The portfolios were analysed using a five year buy-and-hold method after which the overall performance of the two portfolios was consolidated to determine which style outperformed the other. The results of the study indicate support of the international evidence with the local results in some respects achieving far greater returns using the value investment style. This presents an opportunity for private or institutional investors to achieve consistent and abnormal returns on the JSE.Dissertation (MBA)--University of Pretoria, 2010.Gordon Institute of Business Science (GIBS)unrestricte

How Self-Esteem and Executive Control Influence Self-Regulatory Responses to Risk

People with high (HSEs) and low self-esteem (LSEs) often react differently to interpersonal risk. When concerns about their relationship are salient, HSEs seek connection with their partners to quell feelings of vulnerability whereas LSEs distance themselves from their partners to minimize the impact of potential rejection. In the present research, I investigate the extent to which these regulatory dynamics reflect executive-based processes that govern broader regulatory responses. In Studies 1 and 2, HSEs exhibited stronger approach goals (i.e., a greater tendency to pursue rewards and ignore risks) in non-social domains when faced with interpersonal risk whereas LSEs inhibited approach goals and made more conservative decisions. In Studies 3 and 4, I demonstrated that HSEs’ and LSEs’ divergent regulatory responses to risk were contingent on executive control. When participants were cognitively busy, HSEs were less likely to bolster relationship evaluations in the face of interpersonal risk whereas LSEs were more likely to do so. Finally, Study 5 demonstrated that these global regulatory strategies govern HSEs’ and LSEs’ responses to non-interpersonal risk as well. HSEs were more willing to engage in risky social comparison following failure than they were when they received neutral feedback about their performance, whereas LSEs were less willing to compare themselves with others after failure. These effects did not emerge when cognitive resources were depleted. Taken together, the results suggest that HSEs’ and LSEs’ self-regulatory responses to risk are broader and more controlled than previously theorized