Peano High Impedance Surfaces

Following our previous work on metamaterial high-impedance surfaces made of Hilbert curve inclusions, here we theoretically explore the performance of the high-impedance surfaces made of another form of space-filling curve known as the Peano curve. This metamaterial surface, formed by a 2-D periodic arrangement of Peano curve inclusions, is located above a conducting ground plane and is shown to exhibit a high surface impedance surface at certain specific frequencies. Our numerical study reveals the effect of the iteration order of the Peano curve, the surface height above the conducting ground plane and the separation distance between adjacent inclusions.Comment: 16 pages, 9 figures, submitted to Radio Scienc

Molecular phylogenetics of the North American snake tribe Thamnophiini

Advancements in phylogenetic theory and methodology coupled with improvements in computational and sequencing technology facilitate study of the divergence and diversification patterns of life. I apply our current understanding to further explore the relationships and evolution of the North American snake tribe Thamnophiini, as well as to address current topics in phylogenetic and taxonomic methodology. There are two paradigms for the phylogenetic analysis of multi-locus sequence data: one which forces all genes to share the same underlying history, and another that allows genes to follow idiosyncratic patterns of descent from ancestral alleles. The first of these approaches (concatenation) is a simplified model of the actual process of genome evolution while the second (species-tree methods) may be overly complex for histories characterized by long divergence times between cladogenesis. Rather than making an a priori determination concerning which of these phylogenetic models to apply to our data, I seek to provide a framework for choosing between concatenation and species-tree methods that treat genes as independently evolving lineages. In Chapter 2 I demonstrate that parametric bootstrapping can be used to assess the extent to which genealogical incongruence across loci can be attributed to phylogenetic estimation error, and demonstrate the application of our approach using an empirical dataset from 10 species of the Natricine snake sub-family. Since our data exhibit incongruence across loci that is clearly caused by a mixture of coalescent stochasticity and phyogenetic estimation error, we also develop an approach for choosing among species tree estimation methods that take gene trees as input and those that simultaneously estimate gene trees and species trees. Ideally, existing taxonomy would be consistent with phylogenetic estimates derived from rigorously analyzed data using appropriate methods. In Chapter 3 I present a multi-locus molecular analysis of the relationships among nine genera in the North American snake tribe Thamnophiini in order to test the monophyly of the crayfish snakes (genus Regina) and the earth snakes (genus Virginia). Sequence data from seven genes were analyzed to assess relationships among representatives of the nine genera by performing multi-locus phylogeny and species tree estimations, and we performed constraint-based tests of monophyly of classic taxonomic designations on a gene-by-gene basis. Estimates of species trees demonstrate that both genera are paraphyletic, and this inference is supported by a concatenated tree. This finding was supported using gene tree constraint tests and Bayes factors, where we rejected the monophyly of both the crayfish snakes (genus Regina) and the earth snakes (genus Virginia). Progress in our understanding of molecular evolution necessitates a more thorough assessment of the phylogeny of thamnophiine snakes, whose relationships have not been fully resolved, and whose previous phylogenetic estimates are based solely on mitochondrial sequence data. In Chapter 4, I present the most data and taxa robust phylogenetic estimate of Thamnophiini to date, including 50 taxa and sequence data from 8 independently sorting loci. Our findings support the taxonomic recommendations proposed in Chapter 3. Additionally, I estimated the timing of divergence among the three major lineages to have occurred during the Miocene period (~14-11MYA), with higher than expected diversification in the garter snaked during the Pliocene period (~2-6MYA). Finally, we demonstrate that prey choice is labile, and thus an unreliable character for phylogeny reconstruction. Combined, these chapters present a thorough examination of the molecular phylogenetics of thamnophiine snakes. The novel methodological approaches may serve as a guideline for future research. Through estimating a robust phylogeny and suggesting taxonomic changes where appropriate, this work provides a foundation for phylogenetically-based studies of this group

Space-Filling Curve RFID Tags

A completely passive Radio Frequency Tag is proposed, utilizing the scattering from electrically small but resonant inclusions. When placing these space-filling curve inclusions in an array and scaling each element within the array such that each element has its own separate resonant frequency, a radio frequency barcode can be developed from the Radar Cross Section of the array. The narrow bandwidth inherent to such inclusions can be helpful in packing the overall signature into a relatively small frequency spectrum. Such Radio Frequency Tags may have potential use in some applications of Radio Frequency Identification Systems

Radiation Characteristics of Microstrip Dipole Antennas over a High-Impedance Metamaterial Surface made of Hilbert Inclusions

We analyze numerically the radiation characteristics of center-fed microstrip short dipoles and half-wave dipoles near a high-impedance surface made of Hilbert shape flat inclusions. We study the input impedance, pattern and gain of such radiating structures. We show that the radiation resistance of a microstrip dipole increases noticeably at certain frequencies near the resonant frequency of the Hilbert surface. Moreover, antenna gain enhancement at certain frequencies is observed for all dipole sizes we have analyzed

High Impedance Metamaterial Surfaces Using Hilbert-Curve Inclusions

A metamaterial surface, composed of a periodic arrangement of Hilbert Curve inclusions above a conducting ground plane, is analyzed numerically and is shown to possess the properties of a high impedance surface by investigating the phase and magnitude of the reflection coefficient, Γ, for a plane wave of normal incidence. A parametric study is presented with respect to the iteration order of the Hilbert curve, the surface height above the ground plane, and the separation distance between the neighboring Hilbert elements within the surface array

Investigation of Orchard Use Parameters for the Sex Pheromone of the Hickory Shuckworm, Cydia Caryana (Fitch) in Pecan Production

Integrated pest management (IPM) systems provide a necessary alternative to calendar driven, prophylactic applications of pesticides. The use of such systems requires that application of such materials, especially insecticides, be based on knowledge of presence and abundance of the target species. The sex pheromone of Cydia caryana (Fitch), the hickory shuckworm, may be of such use to the commercial pecan producer. The present research was undertaken to delineate practical use parameters for integration of the pheromone into existing pecan IPM systems. To enhance readability and expedite publication, this manuscript has been prepared in publication format. Chapter I (Introduction) advises the reader of the pest species and its biology, the concept of pheromones, and outlines the purposes of the eight investigations undertaken. The eight analyses are subsequently grouped as they will be published. Thus, Chapter II deals with adult emergence patterns, population trends and activity patterns of the species as delineated by pheromone trapping. Chapter III is concerned with trap design and placement under field conditions and Chapter IV with the relationship of pheromone trap capture to fruit infestation. Each of these chapters is presented with an introduction, materials and methods, results and discussion, and a bibliography. Chapter V presents a discussion of some research implications of the previously discussed analyses and contains a bibliography.Entomolog