SMU Digital Repository Copyright (c) 2013 Southern Methodist University All rights reserved. http://digitalrepository.smu.edu Recent documents in SMU Digital Repository en-us Sun, 19 May 2013 01:36:50 PDT 3600 Darwin's Radio Telescope: Use of Genetic Algorithms in the Optimization of Patch Antennas for Radio Astronomy http://digitalrepository.smu.edu/research_day_2013/1 http://digitalrepository.smu.edu/research_day_2013/1 Tue, 05 Mar 2013 13:15:24 PST Radio Astronomy refers to astronomical observation in the radio band of the electromagnetic spectrum and is used by astrophysicists and astronomers to observe parts of the Universe outside of the visible spectrum. Through the use of radio telescopes, astronomers and astrophysicists are able to observe relatively "dark" or "cold" parts of the Universe that are not active within the visible spectrum. The specific event used within this research to observe these areas of cold matter is the 21cm wavelength emission from neutral hydrogen (the H-I line emission). This relatively low energy event allows astronomers to see large gas clouds that would normally be invisible. Radio telescopes are traditionally built out of large dish antenna arrays due to their high resolution and high gain but can be prohibitively expensive and require a great deal of upkeep.

This research focused on using genetic algorithms to optimize a phased array of patch antennas that can add an aspect of versatility and robustness to the radio telescope design that is not provided by a dish antenna radio telescope. Genetic algorithms are a method of design optimization for specific desired outcomes when the relationship between design parameters and effective outcome parameters are not well defined and therefore may result in a non-intuitive optimal design. This method uses the basic rules of evolution in repeated design simulations by rewarding traits that promote a desired effect. In this research, the genetic algorithm controls the spacing and relative weighting of a 2-D array structure for a phased patch antenna array. While the patch antenna does not have the intrinsic properties required for radio astronomy, they can be combined and optimized as a 2-D array structure that provides all the necessary functions of a radio telescope and contains the added benefit of low maintenance and wider viewing angles.

]]> Matthew N. Rispoli Mitigation of Pore Generation in Laser Welding of Magnesium Alloy AZ31B in Lap Joint Configuration http://digitalrepository.smu.edu/engineering_mechanical_research/2 http://digitalrepository.smu.edu/engineering_mechanical_research/2 Thu, 28 Feb 2013 11:32:24 PST Magnesium, as the lightest structural metal, has been widely used in the automotive and aerospace industries. Porosity is the main issue in the welding of magnesium alloys and can be caused by surface coatings, hydrogen gas, pre-existing porosity, the collapse of an unstable keyhole and vaporization of alloying elements. In this study, the effect of the oxide layer on pore generation in the welding of AZ31B-H24 magnesium alloy is investigated. A fiber laser with a power of up to 4 kW is used to weld samples in a lap joint configuration. Two groups of samples are studied: as received (AR) surfaces (where an oxide layer remains on the surface) and treated surfaces. The surface treatment includes two techniques: mechanical removal (MR) and the use of a plasma arc (PA) as a preheating source. Also, a separate set of experiments are designed for preheating samples in a furnace in order to investigate whether the pore mitigation effect of a plasma arc is caused by preheating. Observations include a weld bead profile achieved through optical microscopy, chemical compositions tested by Electron Dispersive Spectroscopy (EDS), and mechanical properties measured with a tensile test. The results obtained show that the preheating effect of a plasma arc procedure can effectively mitigate pore generation. The tensileshear results reveal that PA samples have a higher strength than other groups of samples.

]]> Masoud Harooni et al. Studying the Effect of Laser Welding Parameters on the Quality of ZEK100 Magnesium Alloy Sheets in Lap Joint Configuration http://digitalrepository.smu.edu/engineering_mechanical_research/1 http://digitalrepository.smu.edu/engineering_mechanical_research/1 Wed, 27 Feb 2013 14:08:10 PST Magnesium, as the lightest structural metal, has been widely used in the automotive and aerospace industries. Porosity is the main issue in the welding of magnesium alloys and can be caused by surface coatings, hydrogen gas, pre-existing porosity, the collapse of an unstable keyhole and vaporization of alloying elements. In this study, the effect of the oxide layer on pore generation in the welding of AZ31B-H24 magnesium alloy is investigated. A fiber laser with a power of up to 4 kW is used to weld samples in a lap joint configuration. Two groups of samples are studied: as received (AR) surfaces (where an oxide layer remains on the surface) and treated surfaces. The surface treatment includes two techniques: mechanical removal (MR) and the use of a plasma arc (PA) as a preheating source. Also, a separate set of experiments are designed for preheating samples in a furnace in order to investigate whether the pore mitigation effect of a plasma arc is caused by preheating. Observations include a weld bead profile achieved through optical microscopy, chemical compositions tested by Electron Dispersive Spectroscopy (EDS), and mechanical properties measured with a tensile test. The results obtained show that the preheating effect of a plasma arc procedure can effectively mitigate pore generation. The tensileshear results reveal that PA samples have a higher strength than other groups of samples.

]]> Masoud Harooni et al. Stream: A Framework For Data Stream Modeling in R http://digitalrepository.smu.edu/engineering_compsci_research/3 http://digitalrepository.smu.edu/engineering_compsci_research/3 Wed, 20 Feb 2013 11:25:09 PST In recent years, data streams have become an increasingly important area of research. Common data mining tasks associated with data streams include classification and clustering. Due to both the size and the dynamic nature of data streams, it is often difficult to obtain real-time stream data without the overhead of setting up an infrastructure that will generate data with specific properties. We have built the framework in R, a popular tool for data mining and statistical analysis with the intent that researchers will be able to easily integrate our framework into their existing work. In this paper we introduce the implementation of stream, an R package that provides an intuitive interface for experimenting on data streams and their applications. stream is a general purpose tool that can model data streams and perform data mining tasks on the generated data. It allows the researcher to control specific behaviours of the streams so that they create scenarios that may not be easily reproducible in the real-world, such as the merging and splitting of clusters. Additionally, it has the ability to replay the requested data for other data mining tasks if needed, or read data streams from other sources and incorporate them into the framework.

]]> John Forrest The [Untitled] Festival: Dallas http://digitalrepository.smu.edu/big_ideas_2012_fall/9 http://digitalrepository.smu.edu/big_ideas_2012_fall/9 Wed, 06 Feb 2013 13:19:48 PST James Ryan Jillson et al. Community Participation in Tribal Diabetes Programs http://digitalrepository.smu.edu/hum_sci_anthropology_research/4 http://digitalrepository.smu.edu/hum_sci_anthropology_research/4 Wed, 06 Feb 2013 08:55:51 PST Carolyn Smith-Morris Green Riba http://digitalrepository.smu.edu/big_ideas_2012_fall/8 http://digitalrepository.smu.edu/big_ideas_2012_fall/8 Wed, 06 Feb 2013 08:29:54 PST Rahfin Faruk et al. Open Minds http://digitalrepository.smu.edu/big_ideas_2012_fall/7 http://digitalrepository.smu.edu/big_ideas_2012_fall/7 Wed, 06 Feb 2013 08:14:56 PST Genesis Reed et al. KAIROS Undergraduate Publication http://digitalrepository.smu.edu/big_ideas_2012_fall/6 http://digitalrepository.smu.edu/big_ideas_2012_fall/6 Wed, 06 Feb 2013 07:14:45 PST Arnaud Zimmern et al. STEM Future Dallas http://digitalrepository.smu.edu/big_ideas_2012_fall/5 http://digitalrepository.smu.edu/big_ideas_2012_fall/5 Wed, 06 Feb 2013 06:32:42 PST Jacob Fleming et al. Dallas Refugee Community http://digitalrepository.smu.edu/big_ideas_2012_fall/4 http://digitalrepository.smu.edu/big_ideas_2012_fall/4 Wed, 06 Feb 2013 06:17:22 PST Samantha Matthews et al. Momentum http://digitalrepository.smu.edu/big_ideas_2012_fall/2 http://digitalrepository.smu.edu/big_ideas_2012_fall/2 Thu, 31 Jan 2013 13:25:07 PST Julianna Bond et al. Evaluating hurricane intensity prediction techniques in real time http://digitalrepository.smu.edu/urajournal_research/6 http://digitalrepository.smu.edu/urajournal_research/6 Tue, 29 Jan 2013 05:15:15 PST While the accuracy of hurricane track prediction has been improving, predicting intensity, the maximum sustained wind speed, is still a very difficult challenge. This is problematic because the destructive power of a hurricane is directly related to its intensity. In this paper, we present Prediction Intensity Interval model for Hurricanes (PIIH) which combines sophisticated data mining techniques to create an online real time model for accurate intensity predictions and we present a web-based framework to dynamically compare PIIH to operational models used by the National Hurricane Center (NHC). The created dynamic website tracks, compares, and provides visualization to facilitate immediate comparisons of prediction techniques. This paper is a work in progress paper reporting on both, new features of the PIIH model and online visualization of the accuracy of that model as compared to other techniques.

]]> Vladimir Jovanovic et al. Daniel Senise: Telas - Canvases 1988 - 1994 http://digitalrepository.smu.edu/arts_arthistory_research/5 http://digitalrepository.smu.edu/arts_arthistory_research/5 Mon, 07 Jan 2013 05:51:12 PST Roberto Tejada Carlos Arias: Sobre la mesa http://digitalrepository.smu.edu/arts_arthistory_research/4 http://digitalrepository.smu.edu/arts_arthistory_research/4 Wed, 19 Dec 2012 08:25:14 PST Roberto Tejada The Postmodern Ponzi Scheme: Empirical Analysis of High-Yield Investment Programs http://digitalrepository.smu.edu/engineering_compsci_research/2 http://digitalrepository.smu.edu/engineering_compsci_research/2 Tue, 18 Dec 2012 12:30:18 PST High Yield Investment Program (HYIP) is an online Ponzi scheme, a financial fraud that pays outrageous levels of interest using money from new investors. We call this fraud ‘postmodern’ in that so- phisticated investors understand the fraud, but hope to profit by joining early. These investors support ‘aggregators’ – reputation websites that track the status of HYIPs. We examine 9 months of aggregator data and show that there is no evidence of collusion between different ag- gregators. We use their data to assess HYIP time to collapse, finding – perhaps unsurprisingly – that longer lifetimes are associated with lower interest payments and longer mandatory investment terms. We look at the role of digital currencies in supporting HYIPs, finding that a handful of systems dominate. Finally, we estimate that this type of criminality is turning over at least $6 million/month and set out ways in which it might be disrupted.

]]> Tyler Moore et al. Genetic Algorithms vs. Simulated Annealing: A Comparison of Approaches for Solving the Circuit Partitioning Problem http://digitalrepository.smu.edu/engineering_compsci_research/1 http://digitalrepository.smu.edu/engineering_compsci_research/1 Thu, 13 Dec 2012 05:10:07 PST An important stage in circuit design is placement, where components are assigned to physical locations on a chip. A popular contemporary approach for placement is the use of simulated annealing. While this approach has been shown to produce good placement solutions, recent work in genetic algorithms has produced promising results. The purpose of this study is to determine which approach will result in better placement solutions.

A simplified model of the placement problem, circuit partitioning, was tested on three circuits with both a genetic algorithm and a simulated annealing algorithm. When compared with simulated annealing, the genetic algorithm was found to produce similar results for one circuit, and better results for the other two circuits. Based on these results, genetic algorithms may also yield better results than simulated annealing when applied to the placement problem.

]]> Theodore W. Manikas et al. SYBARITE'S MONASTERY: The Reyes Residence, Mexico City http://digitalrepository.smu.edu/arts_arthistory_research/3 http://digitalrepository.smu.edu/arts_arthistory_research/3 Tue, 30 Oct 2012 08:37:41 PDT Roberto Tejada