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  • 2015-2019  (15)
  • 1
    Publication Date: 2015-08-08
    Description: Large amplitude variations in GPS total electron content (TEC) at Pc5-6 (〈6.67 mHz) frequencies have been observed, using a high data rate Global Positioning System (GPS) receiver of the Canadian High Arctic Ionospheric Network (CHAIN). TEC variations with peak-to-peak amplitudes of 2-7 TEC units (TECU) were observed over a 2.5 hour period in the post-noon sector on 09 September 2011, during a period of high auroral activity within a moderate geomagnetic storm. TEC observations were from the Sanikiluaq, Nunavut (56.54°N, 280.77°E) GPS receiver located in the auroral region. Over this same time period, compressional Pc5-6 magnetic field variations were observed by the geosynchronous GOES 13 magnetometer and the ground-based Sanikiluaq magnetometer. GOES 13 has a northern magnetic footprint in close proximity to Sanikiluaq. Cross correlation analysis indicates that magnetic field and TEC variations were possibly linked. No natural hazards or nuclear explosions capable of exciting TEC perturbations were reported on this day. Using a triangulation technique involving TEC measurements of multiple GPS satellites, the propagation velocity of TEC variations in the ionosphere was also calculated. This calculation revealed two distinct events: lower frequency (~0.9 mHz) TEC variations that propagated westward, consistent with the westward propagation of compressional Pc5 waves observed by GOES 13 and 15 satellites, and higher frequency (~3.3 mHz) TEC variations that propagated southward. This is the first report of variations in ionospheric TEC linked to satellite observations of Pc5-6 ULF waves.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2016-08-30
    Description: This statistical study examines the solar wind dependence of total electron content (TEC) variations arising from mesoscale (10s – 100 s of kms) structuring of the polar cap ionosphere. Six years of TEC measurements were collected from five high-data-rate Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN), from which high resolution magnetic local time-latitude maps of TEC variation occurrence rate and amplitude were created. Ionosonde radars were used to identify TEC variations arising from ionization of the E and F region ionosphere. Statistical TEC maps were examined as a function of solar wind and interplanetary magnetic field (IMF) measurements. Statistical results showed that occurrence rate of TEC variations was highest in localized dayside regions, with exact local time and latitude of peak occurrence depending primarily on the dayside coupling rate of the solar wind and magnetosphere, as well as IMF orientation and magnitude in the Y-Z plane. Occurrence of TEC variations throughout the polar cap increased with solar wind-magnetosphere coupling rate and IMF magnitude. The solar wind dependence of occurrence rate largely reflected the location and rate of dayside magnetic reconnection, and subsequent particle precipitation and polar cap convection. Amplitudes of TEC variations were largest around noon, and increased throughout the polar cap with increased solar wind-magnetosphere coupling rate. These statistical results improve upon the existing observational picture of the polar ionosphere, and will potentially facilitate development of models and techniques for mitigating impacts of the polar ionosphere on navigation signals and communication links.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2016-09-02
    Description: Motivation: A central task of bioinformatics is to develop sensitive and specific means of providing medical prognoses from biomarker patterns. Common methods to predict phenotypes in RNA-Seq datasets utilize machine learning algorithms trained via gene expression. Isoforms, however, generated from alternative splicing, may provide a novel and complementary set of transcripts for phenotype prediction. In contrast to gene expression, the number of isoforms increases significantly due to numerous alternative splicing patterns, resulting in a prioritization problem for many machine learning algorithms. This study identifies the empirically optimal methods of transcript quantification, feature engineering and filtering steps using phenotype prediction accuracy as a metric. At the same time, the complementary nature of gene and isoform data is analyzed and the feasibility of identifying isoforms as biomarker candidates is examined. Results: Isoform features are complementary to gene features, providing non-redundant information and enhanced predictive power when prioritized and filtered. A univariate filtering algorithm, which selects up to the N highest ranking features for phenotype prediction is described and evaluated in this study. An empirical comparison of pipelines for isoform quantification is reported by performing cross-validation prediction tests with datasets from human non-small cell lung cancer (NSCLC) patients, human patients with chronic obstructive pulmonary disease (COPD) and amyotrophic lateral sclerosis (ALS) transgenic mice, each including samples of diseased and non-diseased phenotypes. Availability and Implementation: https://github.com/clabuzze/Phenotype-Prediction-Pipeline.git Contact: clabuzze@iastate.edu , antoniom@bc.edu , watsondk@musc.edu , andersonpe2@cofc.edu
    Print ISSN: 1367-4803
    Electronic ISSN: 1460-2059
    Topics: Biology , Computer Science , Medicine
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  • 4
    Publication Date: 2016-01-29
    Description: Variations in ionospheric total electron content (TEC) associated with ultra-low frequency (ULF) magnetic field variations in the Pc4 (6.7 – 22.0 mHz) frequency band were observed in the early morning sector. TEC variations were observed by the Global Positioning System (GPS) receiver in Sanikiluaq, Nunavut (56.54°N, 280.77°E), which is located near the equatorward edge of the auroral region. Small amplitude Pc4 ULF waves were observed by the Sanikiluaq ground magnetometer and by the geosynchronous GOES 13 satellite. TEC and magnetic field both exhibited narrowband, highly regular, quasi-sinusoidal waveforms, with high correlation and coherence indicating a clear link between TEC variations and Pc4 ULF activity. Variations in TEC and 30–50 keV electron flux observed by GOES 13 were also highly correlated and coherent. TEC variations observed directly above Sanikiluaq were in anti-phase with eastward magnetic field variations on the ground, while TEC variations observed at the footprint of the GOES 13 satellite were in-phase with GOES radial magnetic field and 30–50 keV electron flux. Intermittent occurrence of TEC variations observed by multiple GPS satellites indicated a localized ionospheric response to the Pc4 activity. This is the first clear evidence of a TEC response to these so called “Giant pulsations (Pgs)”. By applying a multi-satellite triangulation technique, the phase velocity, group velocity, and azimuthal wave number of TEC variations was also calculated for an interval of highly coherent measurements. The phase and group propagation velocities were 2–7 km/s and 1–3 km/s north-westward, respectively, while the azimuthal wave number ranged from −35 to −310.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2016-04-29
    Description: This paper presents statistical characteristics (occurrence rate, amplitude, and frequency) of low frequency (〈100 mHz) variations in total electron content (TEC) observed in the polar cap ionosphere. TEC variations were primarily associated with mesoscale (10s-100s of km) ionization structures, and were observed by five Global Positioning System (GPS) receivers over a six year period (2009-2014). The altitude of ionization structures was estimated by using co-located ionosonde radars. High data rate receivers combined with broad spatial coverage of multi-satellite TEC measurements provided high resolution magnetic local time/latitude maps of TEC variation characteristics, which were examined as a function of solar cycle and season. These high resolution maps improve upon the current observational picture of mesoscale structuring in the polar cap, and provide accurate links to particular magnetospheric source regions. Occurrence of TEC variations was consistently highest in dayside regions mapping to low latitude and plasma mantle boundary layers, while largest amplitude TEC variations were observed in dayside regions close to the polar cusp, and lower latitudes around midnight. Occurrence and amplitude of TEC variations increased significantly during the ascending phase of the solar cycle, independent of solar wind conditions, while seasonal statistics showed highest dayside occurrence and amplitude in winter months, lowest in summer, and highest nightside occurrence and amplitude around equinox. A surprising result in the frequency distributions of TEC variations was discrete frequencies of about 2 and 4 mHz, which appeared to originate from regions corresponding to the plasma mantle, immediately poleward of the polar cusp.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2018-04-28
    Description: Transporter gene acquisition and innovation in the evolution of Microsporidia intracellular parasites Transporter gene acquisition and innovation in the evolution of Microsporidia intracellular parasites, Published online: 27 April 2018; doi:10.1038/s41467-018-03923-4 Microsporidia are obligate intracellular parasites that infect both humans and animals. Here, Dean et al. perform ancient gene reconstruction and functional assays to investigate the evolution and functional diversification of nucleotide transporters which are key to the parasite's intracellular lifestyle.
    Electronic ISSN: 2041-1723
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 7
    Publication Date: 2017-05-13
    Description: ABSTRACT Despite the discovery of cryptotephra layers in over 100 peatlands across northern Europe, Holocene cryptotephra layers have not previously been reported from Polish peatlands. Here we present the first Holocene tephra findings from two peatlands in northern Poland. At Bagno Kusowo peatland we identify the most easterly occurrence of the AD 860 B tephra, recently correlated to the White River Ash (WRAe) derived from Mount Churchill, Alaska. A shorter core from Linje peatland contains tephra from the Askja 1875 eruption, extending the spatial distribution and regional importance of this Icelandic tephra in Eastern Europe. Our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on Polish peatlands and contributes towards the development of a regional Holocene tephrostratigraphy for Poland. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.
    Print ISSN: 0267-8179
    Electronic ISSN: 1099-1417
    Topics: Geography , Geosciences
    Published by Wiley
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  • 8
    Publication Date: 2015-03-01
    Description: Recent proteomic studies have identified a novel histone deacetylase complex that is upregulated during mitosis and is associated with cyclin A. This complex is conserved from nematodes to man and contains histone deacetylases 1 and 2, the MIDEAS corepressor protein and a protein called DNTTIP1 whose function was hitherto poorly understood. Here, we report the structures of two domains from DNTTIP1. The amino-terminal region forms a tight dimerization domain with a novel structural fold that interacts with and mediates assembly of the HDAC1:MIDEAS complex. The carboxy-terminal domain of DNTTIP1 has a structure related to the SKI/SNO/DAC domain, despite lacking obvious sequence homology. We show that this domain in DNTTIP1 mediates interaction with both DNA and nucleosomes. Thus, DNTTIP1 acts as a dimeric chromatin binding module in the HDAC1:MIDEAS corepressor complex.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 9
    Publication Date: 2015-11-23
    Print ISSN: 0004-637X
    Electronic ISSN: 1538-4357
    Topics: Physics
    Published by Institute of Physics
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  • 10
    Publication Date: 2018-05-01
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Institute of Physics
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