Searching for Hyperbolicity

This is an expository paper, based on by a talk given at the AWM Research Symposium 2017. It is intended as a gentle introduction to geometric group theory with a focus on the notion of hyperbolicity, a theme that has inspired the field from its inception to current-day research

Detection of Bursts from FRB 121102 with the Effelsberg 100-m Radio Telescope at 5 GHz and the Role of Scintillation

FRB 121102, the only repeating fast radio burst (FRB) known to date, was discovered at 1.4 GHz and shortly after the discovery of its repeating nature, detected up to 2.4 GHz. Here we present three bursts detected with the 100-m Effelsberg radio telescope at 4.85 GHz. All three bursts exhibited frequency structure on broad and narrow frequency scales. Using an autocorrelation function analysis, we measured a characteristic bandwidth of the small-scale structure of 6.4$\pm$1.6 MHz, which is consistent with the diffractive scintillation bandwidth for this line of sight through the Galactic interstellar medium (ISM) predicted by the NE2001 model. These were the only detections in a campaign totaling 22 hours in 10 observing epochs spanning five months. The observed burst detection rate within this observation was inconsistent with a Poisson process with a constant average occurrence rate; three bursts arrived in the final 0.3 hr of a 2 hr observation on 2016 August 20. We therefore observed a change in the rate of detectable bursts during this observation, and we argue that boosting by diffractive interstellar scintillations may have played a role in the detectability. Understanding whether changes in the detection rate of bursts from FRB 121102 observed at other radio frequencies and epochs are also a product of propagation effects, such as scintillation boosting by the Galactic ISM or plasma lensing in the host galaxy, or an intrinsic property of the burst emission will require further observations.Comment: Accepted to ApJ. Minor typos correcte

The RRAT Trap: Interferometric Localization of Radio Pulses from J0628+0909

We present the first blind interferometric detection and imaging of a millisecond radio transient with an observation of transient pulsar J0628+0909. We developed a special observing mode of the Karl G. Jansky Very Large Array (VLA) to produce correlated data products (i.e., visibilities and images) on a time scale of 10 ms. Correlated data effectively produce thousands of beams on the sky that can localize sources anywhere over a wide field of view. We used this new observing mode to find and image pulses from the rotating radio transient (RRAT) J0628+0909, improving its localization by two orders of magnitude. Since the location of the RRAT was only approximately known when first observed, we searched for transients using a wide-field detection algorithm based on the bispectrum, an interferometric closure quantity. Over 16 minutes of observing, this algorithm detected one transient offset roughly 1' from its nominal location; this allowed us to image the RRAT to localize it with an accuracy of 1.6". With a priori knowledge of the RRAT location, a traditional beamforming search of the same data found two, lower significance pulses. The refined RRAT position excludes all potential multiwavelength counterparts, limiting its optical luminosity to L_i'<1.1x10^31 erg/s and excluding its association with a young, luminous neutron star.Comment: Submitted to ApJ, 7 pages, 5 figure

Oceanographic drivers of deep-sea coral species distribution and community assembly on seamounts, islands, atolls, and reefs within the Phoenix Islands Protected Area

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Auscavitch, S. R., Deere, M. C., Keller, A. G., Rotjan, R. D., Shank, T. M., & Cordes, E. E. Oceanographic drivers of deep-sea coral species distribution and community assembly on seamounts, islands, atolls, and reefs within the Phoenix Islands Protected Area. Frontiers in Marine Science, 7, (2020): 42, doi:10.3389/fmars.2020.00042.The Phoenix Islands Protected Area, in the central Pacific waters of the Republic of Kiribati, is a model for large marine protected area (MPA) development and maintenance, but baseline records of the protected biodiversity in its largest environment, the deep sea (>200 m), have not yet been determined. In general, the equatorial central Pacific lacks biogeographic perspective on deep-sea benthic communities compared to more well-studied regions of the North and South Pacific Ocean. In 2017, explorations by the NOAA ship Okeanos Explorer and R/V Falkor were among the first to document the diversity and distribution of deep-water benthic megafauna on numerous seamounts, islands, shallow coral reef banks, and atolls in the region. Here, we present baseline deep-sea coral species distribution and community assembly patterns within the Scleractinia, Octocorallia, Antipatharia, and Zoantharia with respect to different seafloor features and abiotic environmental variables across bathyal depths (200–2500 m). Remotely operated vehicle (ROV) transects were performed on 17 features throughout the Phoenix Islands and Tokelau Ridge Seamounts resulting in the observation of 12,828 deep-water corals and 167 identifiable morphospecies. Anthozoan assemblages were largely octocoral-dominated consisting of 78% of all observations with seamounts having a greater number of observed morphospecies compared to other feature types. Overlying water masses were observed to have significant effects on community assembly across bathyal depths. Revised species inventories further suggest that the protected area it is an area of biogeographic overlap for Pacific deep-water corals, containing species observed across bathyal provinces in the North Pacific, Southwest Pacific, and Western Pacific. These results underscore significant geographic and environmental complexity associated with deep-sea coral communities that remain in under-characterized in the equatorial central Pacific, but also highlight the additional efforts that need to be brought forth to effectively establish baseline ecological metrics in data deficient bathyal provinces.Funding for this work was provided by NOAA Office of Ocean Exploration and Research (Grant No. NA17OAR0110083) to RR, EC, TS, and David Gruber

Crab pulsar giant pulses: Simultaneous radio and GRO observations

Observations are reported of the Crab pulsar made at radio frequencies concurrent with Oriented Scintillation Spectrometer Experiment (OSSE) observations from 15 to 27 May 1991. Using the 43 m telescope at Green Bank at 0.8 and 1.4 GHz, samples were made continuously for 10 hrs/day at intervals of 100 to 300 microsecs. The analysis of the radio data includes calculation of histograms of pulse intensities, absolute timing to about 20 microsec precision, and characterization of intensity variations on time scales from the 33 ms spin period to days. The most detailed analysis is presented made of giant pulses. The ultimate goal is to bin the radio data into giant and nongiant pulses and to form average waveforms of OSSE data for the corresponding pulse periods. A test is done to see whether the violet radio fluctuations (which are not seen in other radio pulsars to the same degree) are correlated with low energy gamma rays, yielding constraints on the radio coherence mechanism and the steadiness of the electron-positron outflow in the magnetosphere. Timing analysis of the radio data provides a well defined ephemeris over the specified range of epochs. The gamma ray pulse phase was predicted with an error of less than 70 microsecs

Educational Quality and County Government Services: Rural Nebraskans\u27 Perceived Impacts of Recent and Proposed Legislation

Many changes have been occurring in rural Nebraska in the area of local finances. Recent school finance legislation has changed the formula that distributes state aid to schools (LB 806) and also imposed new property tax levy limits on school districts (LB 1114). Discussions have also arisen about consolidating county offices and services. Given all these changes, how do rural Nebraskans feel about these issues? How do they feel the new school finance legislation has affected the quality of education in their local school district? Do they support the consolidation of certain county government offices and services with a neighboring county? How do they feel the consolidation of these offices and services will impact the quality of the services they provide? This report details results of 3,036 responses to the 1999 Nebraska Rural Poll, the fourth annual effort to take the pulse of rural Nebraskans. Respondents were asked a series of questions about local finance issues including: their perceptions of the impacts of the new school finance legislation, whether or not they support the consolidation of various county offices and services, and how they feel consolidation would impact the offices’ ability to carry out their functions. Comparisons are made among different subgroups of the respondents, e.g., comparisons by community size, region, income, occupation, etc. Based on these analyses, some key findings emerged: • Forty-three percent of rural Nebraskans believe the quality of education in their local school district has not changed as a result of the changes to the school aid formula. Thirty-four percent believe the quality of education has either greatly decreased or decreased somewhat as a result of these changes, and twenty-three percent believe the quality of education has increased. • Over one-half of rural Nebraskans believe the property tax levy limits have not changed the quality of education in their local school district. Thirty-three percent believe these limits have caused the quality of education to decline, and nine percent believe they have caused the quality to increase. • Respondents with higher educational levels were more likely than those with less education to believe the levy limits had caused the quality of education in their school district to decrease. Forty-six percent of the respondents with a graduate degree believed the levy limits had caused the quality of education to decline in their local school district, but less than one-third of those who had not attended college shared this opinion. • Although the pattern was not entirely consistent, there was some tendency for the following groups to be the most concerned about the quality of education being affected by changes in the school aid formula as well as property tax levy limits: those who have children at home; those who are married; and those age 30 to 49. • Most rural Nebraskans oppose the consolidation of county offices and services. Over onehalf of the respondents opposed the consolidation of six of the eight offices or services listed. The remaining two offices had over forty percent opposing their consolidation. • Most rural Nebraskans believe the consolidation of various county offices with a neighboring county would negatively affect their ability to carry out their functions if they were located in the neighboring county. Over one-half of the respondents believed the consolidations would have a negative impact for seven of the eight offices or services listed. • The two offices and services receiving the most support for consolidation are the county weed superintendent and county jail. Thirty-nine percent supported the consolidation of the county weed superintendent office and thirty-six percent supported the consolidation of the county jail. Support for consolidating the six remaining offices ranged from 21% to 30%. • The offices or services receiving the most opposition toward consolidation are the county sheriff, county treasurer, and county clerk. The proportions opposing the consolidation of each of these offices were 67%, 63% and 61%, respectively. Additionally, at least two-thirds of the respondents believed these offices would lose some of their ability to carry out their functions if they were consolidated and located in a neighboring county. • The groups most likely to oppose consolidation - regardless of the specific office or service under consideration - included the following: those living in communities with less than 500 people, women, those age 65 and older, persons with incomes less than $20,000, the widowed respondents, and those whose education had not gone beyond the high school level

Phylogenetic signal in phonotactics

Phylogenetic methods have broad potential in linguistics beyond tree inference. Here, we show how a phylogenetic approach opens the possibility of gaining historical insights from entirely new kinds of linguistic data – in this instance, statistical phonotactics. We extract phonotactic data from 112 Pama-Nyungan vocabularies and apply tests for phylogenetic signal, quantifying the degree to which the data reflect phylogenetic history. We test three datasets: (1) binary variables recording the presence or absence of biphones (two-segment sequences) in a lexicon (2) frequencies of transitions between segments, and (3) frequencies of transitions between natural sound classes. Australian languages have been characterized as having a high degree of phonotactic homogeneity. Nevertheless, we detect phylogenetic signal in all datasets. Phylogenetic signal is greater in finer-grained frequency data than in binary data, and greatest in natural-class-based data. These results demonstrate the viability of employing a new source of readily extractable data in historical and comparative linguistics.1. Introduction 1.1 Motivations 1.2 Phonotactics as a source of historical signal 2. Phylogenetic signal 3. Materials 3.1 Language sample 3.2 Wordlists 3.3 Reference phylogeny 4. Phylogenetic signal in binary phonotactic data 4.1 Results for binary phonotactic data 4.2 Robustness checks 5. Phylogenetic signal in continuous phonotactic data 5.1 Robustness checks 5.2 Forward transitions versus backward transitions 5.3 Normalization of character values 6. Phylogenetic signal in natural-class-based characters 6.1 Natural-class-based characters versus biphones 7. Discussion 7.1 Overall robustness 7.2 Limitations 8. Conclusio

Leaving the Good Life: Predicting Migration Intentions of Rural Nebraskans

Much has been written about the population turnaround in the nonmetropolitan United States in the 1990\u27s. While only 45% of the nonmetropolitan counties experienced population growth during the 1980\u27s, it was estimated that nearly 74% of the these counties grew between 1990 and 1994 (Johnson, 1996). However, over one-half of Nebraska’s nonmetropolitan counties have continued to experience population declines between 1990 and 1997 (Population Estimates Program, Population Division, U.S. Bureau of the Census, Washington, DC). The question then remains, “Why are people moving from nonmetropolitan counties in Nebraska?” This paper attempts to answer that question by analyzing the migration intentions of nonmetropolitan Nebraskans