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1. Current status of discrete data capture in synoptic surgical pathology and cancer reporting

Author

Williams CL, Bjugn R, and Hassell LA

Subjects
Pathology, RB1-214
Abstract

Christopher L Williams,1 Roger Bjugn,2 Lewis A Hassell1 1Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA; 2Department of Pathology, Oslo University Hospital, Oslo, Norway Abstract: The current status of synoptic pathology reporting is presented with its historical context. The awareness of additional audiences and users has made the presentation and capture of pathology data, particularly cancer data of broad importance. Current models of adoption in the US, Canada, Norway, and the Netherlands are noted. Significant terms, benefits, and stakeholders key to implementation and advancement of capabilities particularly with regard to capture of discrete data elements are presented. Important barriers to be overcome include fiscal constraints, technologic barriers such as interconnectivity and legacy systems, as well as social and organizational obstacles. Keywords: quality assurance, integrated disease reporting, clarity, completeness, pathology report, cancer registry, biorepository

Published
2015

2. Multiscale Characterization of Lignocellulosic Biomass Variability and Its Implications to Preprocessing and Conversion: A Case Study for Corn Stover

Author

Ray, AE, Williams, CL, Hoover, AN, Li, C, Sale, KL, Emerson, RM, Klinger, J, Oksen, E, Narani, A, Yan, J, Beavers, CM, Tanjore, D, Yunes, M, Bose, E, Leal, JH, Bowen, JL, Wolfrum, EJ, Resch, MG, Semelsberger, TA, and Donohoe, BS

Subjects
Biomass variability, Multiscale characterization, Corn stover, k-means clustering, Inorganic speciation, Material attributes, Emergent properties, Analytical Chemistry, Environmental Science and Management, Chemical Engineering
Abstract

Feedstock variability that originates from biomass production and field conditions propagates through the value chain, posing a significant challenge to the emerging biorefinery industry. Variability in feedstock properties impacts feeding, handling, equipment operations, and conversion performance. Feedstock quality attributes, and their variations, are often overlooked in assessing feedstock value and utilization for conversion to fuels, chemicals, and products. This study developed and employed a multiscale analytical characterization approach coupled with data analytic methods to better understand the sources and distribution of feedstock quality variability through evaluation of 24 corn stover bales collected in 4 counties of Iowa. In total, 216 core samples were generated by sampling nine positions on each bale using a reliable bale coring process. The samples were characterized for a broad suite of physicochemical properties ranging across field and bale, macro, micro, and molecular scales. Results demonstrated that feedstock quality attributes can vary at all spatial scales and that multiple sources of variability must be considered in order to establish and manage biomass quality for conversion processes.

Published
2020

3. Best practice recommendations for the use of external telemetry devices on pinnipeds

Author

Horning, M, Andrews, RD, Bishop, AM, Boveng, PL, Costa, DP, Crocker, DE, Haulena, M, Hindell, M, Hindle, AG, Holser, RR, Hooker, SK, Hückstädt, LA, Johnson, S, Lea, MA, McDonald, BI, McMahon, CR, Robinson, PW, Sattler, RL, Shuert, CR, Steingass, SM, Thompson, D, Tuomi, PA, Williams, CL, and Womble, JN

Subjects
Biotelemetry, Biologging, Tagging, Tracking, Marine mammal, Pinniped, Animal welfare, Reduction, Refinement, Replacement, Environmental Science and Management, Ecology, Environmental Engineering
Abstract

Pinnipeds spend large portions of their lives at sea, submerged, or hauled-out on land, often on remote off-shore islands. This fundamentally limits access by researchers to critical parts of pinniped life history and has spurred the development and implementation of a variety of externally attached telemetry devices (ETDs) to collect information about movement patterns, physiology and ecology of marine animals when they cannot be directly observed. ETDs are less invasive and easier to apply than implanted internal devices, making them more widely used. However, ETDs have limited retention times and their use may result in negative short- and long-term consequences including capture myopathy, impacts to energetics, behavior, and entanglement risk. We identify 15 best practice recommendations for the use of ETDs with pinnipeds that address experimental justification, animal capture, tag design, tag attachment, effects assessments, preparation, and reporting. Continued improvement of best practices is critical within the framework of the Three Rs (Reduction, Refinement, Replacement); these best practice recommendations provide current guidance to mitigate known potential negative outcomes for individuals and local populations. These recommendations were developed specifically for pinnipeds; however, they may also be applicable to studies of other marine taxa. We conclude with four desired future directions for the use of ETDs in technology development, validation studies, experimental designs and data sharing.

Published
2019

4. Monitoring, classification, and characterization of interior Alaska forests using AIRSAR and ERS-1 SAR

Author

Williams, CL, McDonald, K, Rignot, E, Viereck, LA, Way, JB, and Zimmermann, R

Subjects
Geography
Abstract

At the Bonanza Creek Experimental Forest (BCEF), past ecological research has been directed at forest successional processes on the floodplain of the Tanana River and adjacent uplands. Research at the Bonanza Creek site continues on the mosaic of forests, shrublands, and wetlands in a wide variety of successional stages on the Tanana floodplain. This paper reviews research since 1988 into the capabilities of Synthetic Aperture Radar (SAR) for monitoring, classification, and characterization of these forests using radar remote sensing and modelling techniques. Classifications of successional stages, obtained by use of different classifiers on multi-frequency and multi-polarimetric AIRSAR data, are contrasted; these classifications have been used to predict classification accuracies obtained with ERS-1 data, and to estimate the utility of an ERS-1 and RADARSAT combination for classification. Forest classifications, used in combination with ground-truth data for more than 50 forest stands, are used to summarize the distribution of biomass on the landscape. This will allow projections of future biomass. Monitoring of forest phenology, seasonality of flooding, and freeze-thaw transitions is ongoing. Also, direct monitoring of dominant tree species is demonstrating diurnal variation and interrelationships among environmental, physiological, and backscatter measurements. © 1995, Cambridge University Press. All rights reserved.

Published
1995

5. Mapping of forest types in Alaskan boreal forests using SAR imagery

Author

Rignot, EJM, Williams, CL, Way, J, and Viereck, LA

Subjects
Life on Land, Geophysics, Electrical and Electronic Engineering, Geomatic Engineering, Geological & Geomatics Engineering
Abstract

Mapping of forest types in the Tanana river flood-plain, interior Alaska, is performed using a maximum-a-posteriori Bayesian classifier applied on SAR data acquired by the NASA/JPL three-frequency polarimetric AIRSAR system on several dates. Five vegetation types are separated, dominated by 1) white spruce, 2) balsam poplar, 3) black spruce, 4) alder/ willow shrubs, and 5) bog/fen/nonforest vegetation. Open water of rivers and lakes is also separated. Accuracy of forest classification is investigated as a function of frequency and polarization of the radar, as well as the forest seasonal state, which includes winter/frozen, winter/thawed, spring/flooded, spring/ unflooded, and summer/dry conditions. Classifications indicate that C-band is a more useful frequency for separating forest types than L or P-bands, and HV polarization is the most useful polarization at all frequencies. The highest classification accuracy, with 90 percent of forest pixels classified correctly, is obtained by combining L-band HV and C-band HV data acquired in spring as seasonal river flooding recedes and before deciduous tree species have leaves. In 17 forest stands for which actual percentages of each tree species are known, the same radar data are capable of predicting tree species composition with less than 10 percent error. For the same combination of observation channels, classification accuracy is 79 percent in spring on a day of intense river flooding, and 62 percent on a dry summer day with leaves on deciduous trees. In winter, using 4-look SAR data instead of 16-look, classification accuracy is 55 percent on a frozen day, and 76 percent on a thawed day. White spruce and balsam poplar stands are best separated in thawed conditions when balsam poplar trees have no leaves. From our classification, we predict that current and future spaceborne SAR systems will have limited mapping capabilities when used alone. Yet, RADARSAT combined with J-ERS-1 and ERS-1 could resolve forest types with 80 percent accuracy, separate nonforest areas resulting from commercial logging or forest wildfire, and map river edges. For comparison, a combination of green, red, and near-infrared radiance data acquired by SPOT-2 on a dry summer day yields a classification accuracy of 83 percent for the same forest stands, with limited success in distinguishing among deciduous forest types and among coniferous forest types. © 1994 IEEE

Published
1994

7. The Murchison Widefield Array Transients Survey (MWATS). A search for low-frequency variability in a bright Southern hemisphere sample

Author

Bell, ME, Murphy, T, Hancock, PJ, Callingham, JR, Johnston, S, Kaplan, DL, Hunstead, RW, Sadler, EM, Croft, S, White, SV, Hurley-Walker, N, Chhetri, R, Morgan, JS, Edwards, PG, Rowlinson, A, Offringa, AR, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Gaensler, BM, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Bell, ME, Murphy, T, Hancock, PJ, Callingham, JR, Johnston, S, Kaplan, DL, Hunstead, RW, Sadler, EM, Croft, S, White, SV, Hurley-Walker, N, Chhetri, R, Morgan, JS, Edwards, PG, Rowlinson, A, Offringa, AR, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Gaensler, BM, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, and Williams, CL

Published
2019

9. Low Altitude Solar Magnetic Reconnection, Type III Solar Radio Bursts, and X-ray Emissions

Author

Cairns, IH, Lobzin, VV, Donea, A, Tingay, SJ, McCauley, PI, Oberoi, D, Duffin, RT, Reiner, MJ, Hurley-Walker, N, Kudryavtseva, NA, Melrose, DB, Harding, JC, Bernardi, G, Bowman, JD, Cappallo, RJ, Corey, BE, Deshpande, A, Emrich, D, Goeke, R, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Ord, SM, Prabu, T, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Wayth, RB, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Cairns, IH, Lobzin, VV, Donea, A, Tingay, SJ, McCauley, PI, Oberoi, D, Duffin, RT, Reiner, MJ, Hurley-Walker, N, Kudryavtseva, NA, Melrose, DB, Harding, JC, Bernardi, G, Bowman, JD, Cappallo, RJ, Corey, BE, Deshpande, A, Emrich, D, Goeke, R, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Ord, SM, Prabu, T, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Wayth, RB, Waterson, M, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

Type III solar radio bursts are the Sun's most intense and frequent nonthermal radio emissions. They involve two critical problems in astrophysics, plasma physics, and space physics: how collective processes produce nonthermal radiation and how magnetic reconnection occurs and changes magnetic energy into kinetic energy. Here magnetic reconnection events are identified definitively in Solar Dynamics Observatory UV-EUV data, with strong upward and downward pairs of jets, current sheets, and cusp-like geometries on top of time-varying magnetic loops, and strong outflows along pairs of open magnetic field lines. Type III bursts imaged by the Murchison Widefield Array and detected by the Learmonth radiospectrograph and STEREO B spacecraft are demonstrated to be in very good temporal and spatial coincidence with specific reconnection events and with bursts of X-rays detected by the RHESSI spacecraft. The reconnection sites are low, near heights of 5-10 Mm. These images and event timings provide the long-desired direct evidence that semi-relativistic electrons energized in magnetic reconnection regions produce type III radio bursts. Not all the observed reconnection events produce X-ray events or coronal or interplanetary type III bursts; thus different special conditions exist for electrons leaving reconnection regions to produce observable radio, EUV, UV, and X-ray bursts.

Published
2018

10. Cancer risk in children born after donor assisted reproductive technology

Author

Williams, CL, Bunch, KJ, Murphy, MFG, Stiller, CA, Bottling, BJ, Wallace, WH, Davies, MC, and Sutcliffe, AG

Abstract

Study question: Do children born after donor assisted reproductive technology (ART) have an increased risk of developing childhood cancer in comparison to the general population? Summary answer: This study showed no overall increased risk of childhood cancer in individuals born after donor ART. What is known already: Most large population based studies have shown no increase in overall childhood cancer incidence after non-donor ART; however other studies have suggested small increased risks in specific cancer types, including haematological cancers. Cancer risk specifically in children born after donor ART has not been investigated to date. Study design, size, duration: This retrospective cohort study utilized record linkage to determine the outcome status of all 12,186 children born in Great Britain (1992-2008) after donor ART. The cohort included 12,137 members contributed 95,389 person-years of follow-up (average follow-up 7.86 years). Participants, setting, methods: Records of all children born in Great Britain (England, Wales, Scotland) after all forms of donor ART (1992-2008) were linked to the UK National Registry of Childhood Tumours (NRCT) to determine the number who subsequently developed cancer by 15 years of age, by the end of 2008. Rates of overall and type specific cancer (selected a priori) were compared with age, sex and calendar year standardised population-based rates, stratifying for potential mediating/moderating factors including sex, age at diagnosis, birth weight, multiple births, maternal previous live births, assisted conception type, and fresh/ cryopreserved cycles. Main results and the role of chance: In our cohort of 12,137 children born after donor assisted reproductive technology (52% male, 55% singleton births), no overall increased risk of cancer was identified. There were 12 cancers detected compared to 14.4 expected (standardised incidence ratio (SIR) 0.83; 95% confidence interval (CI) 0.43-1.45; P=0.50). A small, significant increased risk of hepatoblastoma was found, but the numbers and absolute risks were small (

Published
2017

11. Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

Author

Kapińska, AD, Staveley-Smith, L, Crocker, R, Meurer, GR, Bhandari, S, Hurley-Walker, N, Offringa, AR, Hanish, DJ, Seymour, N, Ekers, RD, Bell, ME, Callingham, JR, Dwarakanath, KS, For, BQ, Gaensler, BM, Hancock, PJ, Hindson, L, Johnston-Hollitt, M, Lenc, E, McKinley, B, Morgan, J, Procopio, P, Wayth, RB, Wu, C, Zheng, Q, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Jacobs, DJ, Kim, HS, Kittiwisit, P, Line, J, Loeb, A, Mitchell, DA, Morales, MF, Neben, AR, Paul, S, Pindor, B, Pober, JC, Riding, J, Sethi, SK, Shankar, NU, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Wyithe, SB, Cappallo, RJ, Deshpande, AA, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, Williams, CL, Kapińska, AD, Staveley-Smith, L, Crocker, R, Meurer, GR, Bhandari, S, Hurley-Walker, N, Offringa, AR, Hanish, DJ, Seymour, N, Ekers, RD, Bell, ME, Callingham, JR, Dwarakanath, KS, For, BQ, Gaensler, BM, Hancock, PJ, Hindson, L, Johnston-Hollitt, M, Lenc, E, McKinley, B, Morgan, J, Procopio, P, Wayth, RB, Wu, C, Zheng, Q, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Jacobs, DJ, Kim, HS, Kittiwisit, P, Line, J, Loeb, A, Mitchell, DA, Morales, MF, Neben, AR, Paul, S, Pindor, B, Pober, JC, Riding, J, Sethi, SK, Shankar, NU, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Wyithe, SB, Cappallo, RJ, Deshpande, AA, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, and Williams, CL

Abstract

© 2017. The American Astronomical Society. All rights reserved. We present new radio continuum observations of NGC 253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC 253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of a central starburst and extended emission. The central component, corresponding to the inner 500 pc of the starburst region of the galaxy, is best modeled as an internally free-free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the spectrum of NGC 253 is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the southeast halo, and may be indicative of synchrotron self-absorption of shock-reaccelerated electrons or an intrinsic low-energy cutoff of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC 253 in our radio images. At 154-231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ∼8 kpc in the z-direction (from the major axis).

Published
2017

12. A large-scale, low-frequency murchison widefield array survey of galactic H II regions between 260 < l < 340

Author

Hindson, L, Johnston-Hollitt, M, Hurley-Walker, N, Callingham, JR, Su, H, Morgan, J, Bell, M, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Dwarakanath, KS, For, BQ, Gaensler, BM, Greenhill, LJ, Hancock, P, Hazelton, BJ, Kapinska, AD, Kaplan, DL, Lenc, E, Lonsdale, CJ, Mckinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, A, Ord, SM, Procopio, P, Prabu, T, Udaya Shankar, N, Srivani, KS, Staveley-Smith, L, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Wu, C, and Zheng, Q

Subjects
Astronomy & Astrophysics
Abstract

© Astronomical Society of Australia 2016. We have compiled a catalogue of H ii regions detected with the Murchison Widefield Array between 72 and 231 MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in H ii regions. We detect 306 H ii regions between 260◦ < l < 340◦ and report on the positions, sizes, peak, integrated flux density, and spectral indices of these H ii regions. By identifying the point at which H ii regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 H ii regions. This catalogue of H ii regions represents the most extensive and uniform low frequency survey of H ii regions in the Galaxy to date.

Published
2016

14. THE SPECTRAL VARIABILITY OF THE GHZ-PEAKED SPECTRUM RADIO SOURCE PKS 1718-649 AND A COMPARISON OF ABSORPTION MODELS

Author

Tingay, SJ, Macquart, J-P, Collier, JD, Rees, G, Callingham, JR, Stevens, J, Carretti, E, Wayth, RB, Wong, GF, Trott, CM, McKinley, B, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Tingay, SJ, Macquart, J-P, Collier, JD, Rees, G, Callingham, JR, Stevens, J, Carretti, E, Wayth, RB, Wong, GF, Trott, CM, McKinley, B, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

Using the new wideband capabilities of the Australia Telescope Compact Array (ATCA), we obtain spectra for PKS 1718-649, a well-known gigahertz-peaked spectrum radio source. The observations, between approximately 1 and 10 GHz over three epochs spanning approximately 21 months, reveal variability both above the spectral peak at ~3 GHz and below the peak. The combination of the low and high frequency variability cannot be easily explained using a single absorption mechanism, such as free-free absorption or synchrotron self-absorption. We find that the PKS 1718-649 spectrum and its variability are best explained by variations in the free-free optical depth on our line-of-sight to the radio source at low frequencies (below the spectral peak) and the adiabatic expansion of the radio source itself at high frequencies (above the spectral peak). The optical depth variations are found to be plausible when X-ray continuum absorption variability seen in samples of Active Galactic Nuclei is considered. We find that the cause of the peaked spectrum in PKS 1718-649 is most likely due to free-free absorption. In agreement with previous studies, we find that the spectrum at each epoch of observation is best fit by a free-free absorption model characterised by a power-law distribution of free-free absorbing clouds. This agreement is extended to frequencies below the 1 GHz lower limit of the ATCA by considering new observations with Parkes at 725 MHz and 199 MHz observations with the newly operational Murchison Widefield Array. These lower frequency observations argue against families of absorption models (both free-free and synchrotron self-absorption) that are based on simple homogenous structures.

Published
2015

15. Ionospheric Modelling using GPS to Calibrate the MWA. I: Comparison of First Order Ionospheric Effects between GPS Models and MWA Observations

Author

Arora, BS, Morgan, J, Ord, SM, Tingay, SJ, Hurley-Walker, N, Bell, M, Bernardi, G, Bhat, NDR, Briggs, F, Callingham, JR, Deshpande, AA, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Hancock, P, Hazelton, BJ, Hindson, L, Jacobs, D, Johnston-Hollitt, M, Kapinska, AD, Kudryavtseva, N, Lenc, E, McKinley, B, Mitchell, D, Oberoi, D, Offringa, AR, Pindor, B, Procopio, P, Riding, J, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Bowman, JD, Cappallo, RJ, Corey, BE, Emrich, D, Goeke, R, Greenhill, LJ, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Morales, MF, Morgan, E, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Arora, BS, Morgan, J, Ord, SM, Tingay, SJ, Hurley-Walker, N, Bell, M, Bernardi, G, Bhat, NDR, Briggs, F, Callingham, JR, Deshpande, AA, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Hancock, P, Hazelton, BJ, Hindson, L, Jacobs, D, Johnston-Hollitt, M, Kapinska, AD, Kudryavtseva, N, Lenc, E, McKinley, B, Mitchell, D, Oberoi, D, Offringa, AR, Pindor, B, Procopio, P, Riding, J, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Bowman, JD, Cappallo, RJ, Corey, BE, Emrich, D, Goeke, R, Greenhill, LJ, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Morales, MF, Morgan, E, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.

Published
2015

16. Measuring phased-array antenna beampatterns with high dynamic range for the Murchison Widefield Array using 137MHz ORBCOMM satellites

Author

Neben, AR, Bradley, RF, Hewitt, JN, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Neben, AR, Bradley, RF, Hewitt, JN, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, and Williams, CL

Published
2015

17. FOREGROUNDS IN WIDE-FIELD REDSHIFTED 21 cm POWER SPECTRA

Author

Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Corey, BE, de Oliveira-Costa, A, Dillon, JS, Emrich, D, Ewall-Wice, A, Feng, L, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kim, H-S, Kittiwisit, P, Kratzenberg, E, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Wu, C, Wyithe, JSB, Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Corey, BE, de Oliveira-Costa, A, Dillon, JS, Emrich, D, Ewall-Wice, A, Feng, L, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kim, H-S, Kittiwisit, P, Kratzenberg, E, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Wu, C, and Wyithe, JSB

Abstract

Detection of 21~cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic "pitchfork" signature on the "foreground wedge" in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor ~100 with negligible loss of sensitivity.

Published
2015

18. Limits on low-frequency radio emission from southern exoplanets with the Murchison Widefield Array

Author

Murphy, T, Bell, ME, Kaplan, DL, Gaensler, BM, Offringa, AR, Lenc, E, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, DA, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Murphy, T, Bell, ME, Kaplan, DL, Gaensler, BM, Offringa, AR, Lenc, E, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, DA, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We present the results of a survey for low frequency radio emission from 17 known exoplanetary systems with the Murchison Widefield Array. This sample includes 13 systems that have not previously been targeted with radio observations. We detected no radio emission at 154 MHz, and put 3 sigma upper limits in the range 15.2-112.5 mJy on this emission. We also searched for circularly polarised emission and made no detections, obtaining 3 sigma upper limits in the range 3.4-49.9 mJy. These are comparable with the best low frequency radio limits in the existing literature and translate to luminosity limits of between 1.2 x 10^14 W and 1.4 x 10^17 W if the emission is assumed to be 100% circularly polarised. These are the first results from a larger program to systematically search for exoplanetary emission with the MWA.

Published
2015

19. Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array

Author

Loi, ST, Trott, CM, Murphy, T, Cairns, IH, Bell, M, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Feng, L, Hancock, PJ, Kaplan, DL, Kudryavtseva, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Loi, ST, Trott, CM, Murphy, T, Cairns, IH, Bell, M, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Feng, L, Hancock, PJ, Kaplan, DL, Kudryavtseva, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Published
2015

20. Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array

Author

Loi, ST, Murphy, T, Bell, ME, Kaplan, DL, Lenc, E, Offringa, AR, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Loi, ST, Murphy, T, Bell, ME, Kaplan, DL, Lenc, E, Offringa, AR, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Published
2015

21. Real-time imaging of density ducts between the plasmasphere and ionosphere

Author

Loi, ST, Murphy, T, Cairns, IH, Menk, FW, Waters, CL, Erickson, PJ, Trott, CM, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Bell, ME, Ekers, RD, Gaensler, BM, Lonsdale, CJ, Feng, L, Hancock, PJ, Kaplan, DL, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Loi, ST, Murphy, T, Cairns, IH, Menk, FW, Waters, CL, Erickson, PJ, Trott, CM, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Bell, ME, Ekers, RD, Gaensler, BM, Lonsdale, CJ, Feng, L, Hancock, PJ, Kaplan, DL, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, and Williams, CL

Published
2015

22. MURCHISON WIDEFIELD ARRAY OBSERVATIONS OF ANOMALOUS VARIABILITY: A SERENDIPITOUS NIGHT-TIME DETECTION OF INTERPLANETARY SCINTILLATION

Author

Kaplan, DL, Tingay, SJ, Manoharan, PK, Macquart, JP, Hancock, P, Morgan, J, Mitchell, DA, Ekers, RD, Wayth, RB, Trott, C, Murphy, T, Oberoi, D, Cairns, IH, Feng, L, Kudryavtseva, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Gaensler, BM, Greenhill, LJ, Walker, NH, Hazelton, BJ, Hollitt, MJ, Lonsdale, CJ, McWhirter, SR, Morales, MF, Morgan, E, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Webster, RL, Williams, A, Williams, CL, Kaplan, DL, Tingay, SJ, Manoharan, PK, Macquart, JP, Hancock, P, Morgan, J, Mitchell, DA, Ekers, RD, Wayth, RB, Trott, C, Murphy, T, Oberoi, D, Cairns, IH, Feng, L, Kudryavtseva, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Gaensler, BM, Greenhill, LJ, Walker, NH, Hazelton, BJ, Hollitt, MJ, Lonsdale, CJ, McWhirter, SR, Morales, MF, Morgan, E, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Webster, RL, Williams, A, and Williams, CL

Published
2015

23. The Murchison Widefield Array Correlator

Author

Ord, SM, Crosse, B, Emrich, D, Pallot, D, Wayth, RB, Clark, MA, Tremblay, SE, Arcus, W, Barnes, D, Bell, M, Bernardi, G, Bhat, NDR, Bowman, JD, Briggs, F, Bunton, JD, Cappallo, RJ, Corey, BE, Deshpande, AA, deSouza, L, Ewell-Wice, A, Feng, L, Goeke, R, Greenhill, LJ, Hazelton, BJ, Herne, D, Hewitt, JN, Hindson, L, Hurley-Walker, N, Jacobs, D, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kincaid, BB, Koenig, R, Kratzenberg, E, Kudryavtseva, N, Lenc, E, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, A, Pathikulangara, J, Pindor, B, Prabu, T, Procopio, P, Remillard, RA, Riding, J, Rogers, AEE, Roshi, A, Salah, JE, Sault, RJ, Shankar, NU, Srivani, KS, Stevens, J, Subrahmanyan, R, Tingay, SJ, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Wyithe, JSB, Ord, SM, Crosse, B, Emrich, D, Pallot, D, Wayth, RB, Clark, MA, Tremblay, SE, Arcus, W, Barnes, D, Bell, M, Bernardi, G, Bhat, NDR, Bowman, JD, Briggs, F, Bunton, JD, Cappallo, RJ, Corey, BE, Deshpande, AA, deSouza, L, Ewell-Wice, A, Feng, L, Goeke, R, Greenhill, LJ, Hazelton, BJ, Herne, D, Hewitt, JN, Hindson, L, Hurley-Walker, N, Jacobs, D, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kincaid, BB, Koenig, R, Kratzenberg, E, Kudryavtseva, N, Lenc, E, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, A, Pathikulangara, J, Pindor, B, Prabu, T, Procopio, P, Remillard, RA, Riding, J, Rogers, AEE, Roshi, A, Salah, JE, Sault, RJ, Shankar, NU, Srivani, KS, Stevens, J, Subrahmanyan, R, Tingay, SJ, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, and Wyithe, JSB

Abstract

The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day−1 of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces.

Published
2015

24. The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

Author

Offringa, AR, Wayth, RB, Hurley-Walker, N, Kaplan, DL, Barry, N, Beardsley, AP, Bell, ME, Bernardi, G, Bowman, JD, Briggs, F, Callingham, JR, Cappallo, RJ, Carroll, P, Deshpande, AA, Dillon, JS, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Gaensler, BM, Greenhill, LJ, Hancock, P, Hazelton, BJ, Hewitt, JN, Hindson, L, Jacobs, DC, Johnston-Hollitt, M, Kapinska, AD, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Morgan, J, Neben, AR, Oberoi, D, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, S, Srivani, KS, Staveley-Smith, L, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Williams, A, Williams, CL, Wu, C, Wyithe, JS, Zheng, Q, Offringa, AR, Wayth, RB, Hurley-Walker, N, Kaplan, DL, Barry, N, Beardsley, AP, Bell, ME, Bernardi, G, Bowman, JD, Briggs, F, Callingham, JR, Cappallo, RJ, Carroll, P, Deshpande, AA, Dillon, JS, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Gaensler, BM, Greenhill, LJ, Hancock, P, Hazelton, BJ, Hewitt, JN, Hindson, L, Jacobs, DC, Johnston-Hollitt, M, Kapinska, AD, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Morgan, J, Neben, AR, Oberoi, D, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, S, Srivani, KS, Staveley-Smith, L, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Williams, A, Williams, CL, Wu, C, Wyithe, JS, and Zheng, Q

Abstract

The Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).

Published
2015

25. Empirical covariance modeling for 21 cm power spectrum estimation: A method demonstration and new limits from early Murchison Widefield Array 128-tile data

Author

Dillon, JS, Neben, AR, Hewitt, JN, Tegmark, M, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, de Oliveira-Costa, A, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hurley-Walker, N, Jacobs, DC, Kim, HS, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, McKinley, B, Mitchell, DA, Morales, MF, Offringa, AR, Paul, S, Pindor, B, Pober, JC, Procopio, P, Riding, J, Sethi, S, Shankar, NU, Subrahmanyan, R, Sullivan, I, Thyagarajan, N, Tingay, SJ, Trott, C, Wayth, RB, Webster, RL, Wyithe, S, Bernardi, G, Cappallo, RJ, Deshpande, AA, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, Williams, CL, Dillon, JS, Neben, AR, Hewitt, JN, Tegmark, M, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, de Oliveira-Costa, A, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hurley-Walker, N, Jacobs, DC, Kim, HS, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, McKinley, B, Mitchell, DA, Morales, MF, Offringa, AR, Paul, S, Pindor, B, Pober, JC, Procopio, P, Riding, J, Sethi, S, Shankar, NU, Subrahmanyan, R, Sullivan, I, Thyagarajan, N, Tingay, SJ, Trott, C, Wayth, RB, Webster, RL, Wyithe, S, Bernardi, G, Cappallo, RJ, Deshpande, AA, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, and Williams, CL

Abstract

The separation of the faint cosmological background signal from bright astrophysical foregrounds remains one of the most daunting challenges of mapping the high-redshift intergalactic medium with the redshifted 21 cm line of neutral hydrogen. Advances in mapping and modeling of diffuse and point source foregrounds have improved subtraction accuracy, but no subtraction scheme is perfect. Precisely quantifying the errors and error correlations due to missubtracted foregrounds allows for both the rigorous analysis of the 21 cm power spectrum and for the maximal isolation of the "EoR window" from foreground contamination. We present a method to infer the covariance of foreground residuals from the data itself in contrast to previous attempts at a priori modeling. We demonstrate our method by setting limits on the power spectrum using a 3 h integration from the 128-tile Murchison Widefield Array. Observing between 167 and 198 MHz, we find at 95% confidence a best limit of Delta^2(k) < 3.7 x 10^4 mK^2 at comoving scale k = 0.18 hMpc^-1 and at z = 6.8, consistent with existing limits.

Published
2015

26. An analysis of the halo and relic radio emission from Abell 3376 from Murchison Widefield Array observations

Author

George, LT, Dwarakanath, KS, Johnston-Hollitt, M, Hurley-Walker, N, Hindson, L, Kapinska, AD, Tingay, SJ, Bell, M, Callingham, JR, For, B-Q, Hancock, PJ, Lenc, E, McKinley, B, Morgan, J, Offringa, A, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, George, LT, Dwarakanath, KS, Johnston-Hollitt, M, Hurley-Walker, N, Hindson, L, Kapinska, AD, Tingay, SJ, Bell, M, Callingham, JR, For, B-Q, Hancock, PJ, Lenc, E, McKinley, B, Morgan, J, Offringa, A, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We have carried out multiwavelength observations of the near-by ($z=0.046$) rich, merging galaxy cluster Abell 3376 with the Murchison Widefield Array (MWA). As a part of the GaLactic and Extragalactic All-sky MWA survey (GLEAM), this cluster was observed at 88, 118, 154, 188 and 215 MHz. The known radio relics, towards the eastern and western peripheries of the cluster, were detected at all the frequencies. The relics, with a linear extent of $\sim$ 1 Mpc each, are separated by $\sim$ 2 Mpc. Combining the current observations with those in the literature, we have obtained the spectra of these relics over the frequency range 80 -- 1400 MHz. The spectra follow power laws, with $\alpha$ = $-1.17\pm0.06$ and $-1.37\pm0.08$ for the west and east relics, respectively ($S \propto \nu^{\alpha}$). Assuming the break frequency to be near the lower end of the spectrum we estimate the age of the relics to be $\sim$ 0.4 Gyr. No diffuse radio emission from the central regions of the cluster (halo) was detected. The upper limit on the radio power of any possible halo that might be present in the cluster is a factor of 35 lower than that expected from the radio power and X-ray luminosity correlation for cluster halos. From this we conclude that the cluster halo is very extended ($>$ 500 kpc) and/or most of the radio emission from the halo has decayed. The current limit on the halo radio power is a factor of ten lower than the existing upper limits with possible implications for models of halo formation.

Published
2015

27. CONFIRMATION OF WIDE-FIELD SIGNATURES IN REDSHIFTED 21 cm POWER SPECTRA

Author

Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Deshpande, AA, de Oliveira-Costa, A, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Wyithe, JSB, Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Deshpande, AA, de Oliveira-Costa, A, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Wayth, RB, Webster, RL, Williams, A, Williams, CL, and Wyithe, JSB

Abstract

We confirm our recent prediction of the "pitchfork" foreground signature in power spectra of high-redshift 21 cm measurements where the interferometer is sensitive to large-scale structure on all baselines. This is due to the inherent response of a wide-field instrument and is characterized by enhanced power from foreground emission in Fourier modes adjacent to those considered to be the most sensitive to the cosmological H I signal. In our recent paper, many signatures from the simulation that predicted this feature were validated against Murchison Widefield Array (MWA) data, but this key pitchfork signature was close to the noise level. In this paper, we improve the data sensitivity through the coherent averaging of 12 independent snapshots with identical instrument settings and provide the first confirmation of the prediction with a signal-to-noise ratio > 10. This wide-field effect can be mitigated by careful antenna designs that suppress sensitivity near the horizon. Simple models for antenna apertures that have been proposed for future instruments such as the Hydrogen Epoch of Reionization Array and the Square Kilometre Array indicate they should suppress foreground leakage from the pitchfork by ~40 dB relative to the MWA and significantly increase the likelihood of cosmological signal detection in these critical Fourier modes in the three-dimensional power spectrum.

Published
2015

28. A SEARCH FOR FAST RADIO BURSTS AT LOW FREQUENCIES WITH MURCHISON WIDEFIELD ARRAY HIGH TIME RESOLUTION IMAGING

Author

Tingay, SJ, Trott, CM, Wayth, RB, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Feng, L, Gaensler, BM, Greenhill, LJ, Hancock, PJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Murphy, T, Oberoi, D, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Webster, RL, Williams, A, Williams, CL, Tingay, SJ, Trott, CM, Wayth, RB, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Feng, L, Gaensler, BM, Greenhill, LJ, Hancock, PJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Murphy, T, Oberoi, D, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Webster, RL, Williams, A, and Williams, CL

Published
2015

29. BROADBAND SPECTRAL MODELING OF THE EXTREME GIGAHERTZ-PEAKED SPECTRUM RADIO SOURCE PKS B0008-421

Author

Callingham, JR, Gaensler, BM, Ekers, RD, Tingay, SJ, Wayth, RB, Morgan, J, Bernardi, G, Bell, ME, Bhat, R, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hindson, L, Hurley-Walker, N, Jacobs, DC, Johnston-Hollitt, M, Kaplan, DL, Kudrayvtseva, N, Lenc, E, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, AR, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Riding, J, Srivani, KS, Subrahmanyan, R, Shankar, NU, Webster, RL, Williams, A, Williams, CL, Callingham, JR, Gaensler, BM, Ekers, RD, Tingay, SJ, Wayth, RB, Morgan, J, Bernardi, G, Bell, ME, Bhat, R, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hindson, L, Hurley-Walker, N, Jacobs, DC, Johnston-Hollitt, M, Kaplan, DL, Kudrayvtseva, N, Lenc, E, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, AR, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Riding, J, Srivani, KS, Subrahmanyan, R, Shankar, NU, Webster, RL, Williams, A, and Williams, CL

Abstract

We present broadband observations and spectral modeling of PKS B0008-421, and identify it as an extreme gigahertz-peaked spectrum (GPS) source. PKS B0008-421 is characterized by the steepest known spectral slope below the turnover, close to the theoretical limit of synchrotron self-absorption, and the smallest known spectral width of any GPS source. Spectral coverage of the source spans from 0.118 to 22 GHz, which includes data from the Murchison Widefield Array and the wide bandpass receivers on the Australia Telescope Compact Array. We have implemented a Bayesian inference model fitting routine to fit the data with various absorption models. We find that without the inclusion of a high-frequency exponential break the absorption models can not accurately fit the data, with significant deviations above and below the peak in the radio spectrum. The addition of a high-frequency break provides acceptable spectral fits for the inhomogeneous free-free absorption and double-component synchrotron self-absorption models, with the inhomogeneous free-free absorption model statistically favored. The requirement of a high-frequency spectral break implies that the source has ceased injecting fresh particles. Additional support for the inhomogeneous free-free absorption model as being responsible for the turnover in the spectrum is given by the consistency between the physical parameters derived from the model fit and the implications of the exponential spectral break, such as the necessity of the source being surrounded by a dense ambient medium to maintain the peak frequency near the gigahertz region. The discovery of PKS B0008-421 suggests that the next generation of low radio frequency surveys could reveal a large population of GPS sources that have ceased activity, and that a portion of the ultra-steep spectrum source population could be composed of these GPS sources in a relic phase.

Published
2015

30. SIMULTANEOUS OBSERVATIONS OF GIANT PULSES FROM THE CRAB PULSAR, WITH THE MURCHISON WIDEFIELD ARRAY AND PARKES RADIO TELESCOPE: IMPLICATIONS FOR THE GIANT PULSE EMISSION MECHANISM

Author

Oronsaye, SI, Ord, SM, Bhat, NDR, Tremblay, SE, McSweeney, SJ, Tingay, SJ, van Straten, W, Jameson, A, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Oronsaye, SI, Ord, SM, Bhat, NDR, Tremblay, SE, McSweeney, SJ, Tingay, SJ, van Straten, W, Jameson, A, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Wayth, RB, Webster, RL, Williams, A, and Williams, CL

Published
2015

31. Nachweis und Bestimmung des Eisens, sowie seine Trennung von anderen Elementen

Author

Houben, J., Meyer, Julius, Treadwell, F. P., Heeren, F., Martin, H. G., Williams, Cl. E., Anderson, Arvid E., Sims, C. E., Larsen, B. M., Terres, E., Pongracz, A., Ingeberg, H. C. M., Foerster, F., Herold, V., Peck, E. S., Frerichs, G., Coblentz, V., May, O. B., Horlück, A. D., Eberhard, A., Schmidt, E., Wüst, Fr., Kirpach, N., Schneider, L., Parry, J., Morgan, J. J., Diepschlag, E., and Edgar Thompson Steel Works

Published
1927
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32. Artificial selection on egg size perturbs early pattern formation in Drosophila melanogaster

Author

Miles, CM, Lott, SE, Luengo Hendriks, CL, Ludwig, MZ, Manu, Williams, CL, and Kreitman, M

Subjects
Homeodomain Proteins, Evolutionary Biology, animal structures, segmentation patterning, Ecology, fungi, Genetic Variation, robustness, Biological Evolution, Drosophila melanogaster, Gene Expression Regulation, Genes, Genetic, embryonic structures, Cell number, Animals, Drosophila Proteins, Blastoderm, Developmental, Female, Insect, Selection, Ovum, Transcription Factors, Body Patterning
Abstract

Pattern formation in Drosophila embryogenesis has been widely investigated as a developmental and evolutionary model of robustness. To ask whether genetic variation for pattern formation is suppressed in this system, artificial selection for divergent egg size was used to challenge the scaling of even-skipped (eve) pattern formation in mitotic cycle 14 (stage 5) embryos of Drosophila melanogaster. Three-dimensional confocal imaging revealed shifts in the allometry of eve pair-rule stripes along both anterior-posterior (A-P) and dorsoventral (D-V) axes as a correlated response to egg size selection, indicating the availability of genetic variation for this buffered trait. Environmental perturbation was not required for the manifestation of this variation. The number of nuclei at the cellular blastoderm stage also changed in response to selection, with large-egg selected lines having more than 1000 additional nuclei relative to small-egg lines. This increase in nuclear number in larger eggs does not scale with egg size, however, as nuclear density is inversely correlated with egg length. Nuclear density varies along the A-P axis but does not correlate with the shift in eve stripe allometry between the selection treatments. Despite its macroevolutionary conservation, both eve stripe patterning and blastoderm cell number vary genetically both within and between closely related species. © 2010 The Author(s). Evolution © 2010 The Society for the Study of Evolution.

Published
2011

33. The First Murchison Widefield Array low-frequency radio observations of cluster scale non-thermal emission: the case of Abell 3667

Author

Hindson, L, Johnston-Hollitt, M, Hurley-Walker, N, Buckley, K, Morgan, J, Carretti, E, Dwarakanath, KS, Bell, M, Bernardi, G, Bhat, NDR, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Ewall-Wice, A, Feng, L, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Jacobs, D, Kaplan, DL, Kasper, JC, Kratzenberg, E, Kudryavtseva, N, Lenc, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, McKinley, B, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Offringa, AR, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Hindson, L, Johnston-Hollitt, M, Hurley-Walker, N, Buckley, K, Morgan, J, Carretti, E, Dwarakanath, KS, Bell, M, Bernardi, G, Bhat, NDR, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Ewall-Wice, A, Feng, L, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Jacobs, D, Kaplan, DL, Kasper, JC, Kratzenberg, E, Kudryavtseva, N, Lenc, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, McKinley, B, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Offringa, AR, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We present the first Murchison Widefield Array observations of the well-known cluster of galaxies Abell 3667 (A3667) between 105 and 241 MHz. A3667 is one of the best known examples of a galaxy cluster hosting a double radio relic and has been reported to contain a faint radio halo and bridge. The origins of radio halos, relics and bridges is still unclear, however galaxy cluster mergers seems to be an important factor. We clearly detect the North-West (NW) and South-East (SE) radio relics in A3667 and find an integrated flux density at 149 MHz of 28.1 +/- 1.7 and 2.4 +/- 0.1 Jy, respectively, with an average spectral index, between 120 and 1400 MHz, of -0.9 +/- 0.1 for both relics. We find evidence of a spatial variation in the spectral index across the NW relic steepening towards the centre of the cluster, which indicates an ageing electron population. These properties are consistent with higher frequency observations. We detect emission that could be associated with a radio halo and bridge. How- ever, due to the presence of poorly sampled large-scale Galactic emission and blended point sources we are unable to verify the exact nature of these features.

Published
2014

34. STUDY OF REDSHIFTED H I FROM THE EPOCH OF REIONIZATION WITH DRIFT SCAN

Author

Paul, S, Sethi, SK, Subrahmanyan, R, Shankar, NU, Dwarakanath, KS, Deshpande, AA, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Emrich, D, Gaensler, BM, Goeke, RF, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, EH, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, AA, Srivani, KS, Tingay, SJ, Wayth, RB, Waterson, M, Webster, RL, Whitney, AR, Williams, AJ, Williams, CL, Paul, S, Sethi, SK, Subrahmanyan, R, Shankar, NU, Dwarakanath, KS, Deshpande, AA, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Emrich, D, Gaensler, BM, Goeke, RF, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, EH, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, AA, Srivani, KS, Tingay, SJ, Wayth, RB, Waterson, M, Webster, RL, Whitney, AR, Williams, AJ, and Williams, CL

Abstract

The detection of the Epoch of Reionization (EoR) in the redshifted 21-cm line is a challenging task. Here we formulate the detection of the EoR signal using the drift scan strategy. This method potentially has better instrumental stability as compared to the case where a single patch of sky is tracked. We demonstrate that the correlation time between measured visibilities could extend up to 1-2 hr for an interferometer array such as the Murchison Widefield Array (MWA), which has a wide primary beam. We estimate the EoR power based on cross-correlation of visibilities across time and show that the drift scan strategy is capable of the detection of the EoR signal with comparable/better signal-to-noise as compared to the tracking case. We also estimate the visibility correlation for a set of bright point sources and argue that the statistical inhomogeneity of bright point sources might allow their separation from the EoR signal.

Published
2014

35. Observing the Sun with the Murchison Widefield Array

Author

Oberoi, D, Sharma, R, Bhatnagar, S, Lonsdale, CJ, Matthews, LD, Cairns, IH, Tingay, SJ, Benkevitch, L, Donea, A, White, SM, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, A, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Offringa, AR, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Salah, JE, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, William, A, Williams, CL, Oberoi, D, Sharma, R, Bhatnagar, S, Lonsdale, CJ, Matthews, LD, Cairns, IH, Tingay, SJ, Benkevitch, L, Donea, A, White, SM, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, A, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Offringa, AR, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Salah, JE, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, William, A, and Williams, CL

Published
2014

36. THE LOW-FREQUENCY CHARACTERISTICS OF PSR J0437-4715 OBSERVED WITH THE MURCHISON WIDE-FIELD ARRAY

Author

Bhat, NDR, Ord, SM, Tremblay, SE, Tingay, SJ, Deshpande, AA, van Straten, W, Oronsaye, S, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Prabu, T, Rogers, AEE, Roshi, DA, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Bhat, NDR, Ord, SM, Tremblay, SE, Tingay, SJ, Deshpande, AA, van Straten, W, Oronsaye, S, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Prabu, T, Rogers, AEE, Roshi, DA, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Published
2014

38. Development and testing of the Alzheimer's disease and related dementias mood scale.

Author

Tappen RM and Williams CL

Abstract

BACKGROUND:: Existing mood measures for individuals with Alzheimer's disease and related dementias (AD-RD) focus primarily on negative moods, including depression. OBJECTIVE:: The objectives of this study were to design and test a new measure of both positive and negative moods in individuals aged 55 years or older with mild to severe AD-RD. METHODS:: Formal and informal caregivers' observations of mood in this population generated 26 positive and 27 negative mood descriptors reviewed by content experts before pilot testing. The AD-RD Mood Scale and Mini-Mental State Examination were administered to 298 participants with very mild to severe cognitive impairment. Two examiners simultaneously rated a subsample of participants, a second subsample was retested after 2 weeks, and additional mood measures were administered to a third subsample. RESULTS:: The final AD-RD Mood Scale contains 34 items in two positive subscales (spirited and contented) and three negative subscales (hostile, apathetic, and sad). The five subscales explain 82% of the variance. Cronbach's alpha values were .92, .90, .85, .77, and .73 for the spirited, hostile, contented, apathetic, and sad subscales, respectively. Interrater reliability ranged from .88 to .63. Mean subscale scores were stable over time. Moderate to strong validity coefficients (Pearson's r) produced by comparison with four existing measures were in the hypothesized direction. Subscale scores discriminated between participants who are depressed and those who are nondepressed. DISCUSSION:: The final 34-item AD-RD Mood Scale provides useful data on both positive and negative moods of individuals with AD-RD. Further evaluation of reliability and validity in a multiethnic sample is recommended, as are confirmatory factor analysis and expansion to add subscales related to tension and social unease. [ABSTRACT FROM AUTHOR]

Published
2008
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39. Workers' compensation for psychological injury: demographic and work-related correlates.

Author

Haines J, Williams CL, and Carson J

Abstract

This study aimed to determine the demographic and work-related factors that contributed to the filing of a workers' compensation claim for psychological injury. Four groups of employees were compared: those who filed a workers' compensation claim, those who sought psychological treatment for occupational stress but did not file a workers' compensation claim, those who experienced elevated stress levels but did not seek help or lodge a claim, and those who experienced stressful events at work but did not develop symptomatology. The results indicated few variables that could adequately explain why some stressed employees opted for a workers' compensation claim. The implications of these results are discussed. [ABSTRACT FROM AUTHOR]

Published
2006

40. Qualitative and quantitative measurement of depression in veterans recovering from stroke.

Author

Williams CL, Rittman MR, Boylstein C, Faircloth C, and Haijing Q

Abstract

This analysis triangulates qualitative and quantitative data from interviews, Geriatric Depression Scale scores, and patient records to evaluate poststroke depression. Participants were veterans who were discharged home following a new stroke. Findings indicated underrecognition and treatment of depression. Narrative data uncovered a rich description of respondents' perceptions and emotional experiences during stroke recovery. [ABSTRACT FROM AUTHOR]

Published
2005
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43. Workers' compensation for psychological injury: personal and environmental correlates.

Author

Haines J, Williams CL, and Carson J

Abstract

The aim of this study was to determine the personal and environmental factors that contribute to the lodging of a workers' compensation claim for psychological injury. Four groups were compared: individuals who had lodged a workers' compensation claim, people who had sought psychological assistance for the management of work-related stress reactions but who had not lodged a workers' compensation claim; people who had experienced stress symptoms but who had not lodged a claim or sought help; and people who experienced stressful work events but who had not developed symptoms. Examination was made of cognitive distortion, irrational beliefs and coping resources as individual factors, and stressful life events, daily hassles and work environment factors as environmental variables. The Compensation group was distinguished from other groups only on the basis of work environmental factors. The implications of these results in the understanding of the decision to lodge a workers' compensation claim are considered. [ABSTRACT FROM AUTHOR]

Published
2004

44. The measurement of wisdom and its relationship to adolescent substance use and problem behaviors.

Author

Perry CL, Komro KA, Jones RM, Munson K, Williams CL, and Jason L

Abstract

The objective of this study was to create an Adolescent Wisdom Scale, based on Jason et al.'s (in press) Functional Value Scale. The Adolescent Wisdom Scale is a self-rating of 23 attributes that have been shown to be associated with people who are perceived to have wisdom. The sample of 2,027 high school seniors, from 20 school districts in northeastern Minnesota, was administered a survey in spring 1998, as part of an ongoing alcohol use prevention program. The scale was found to have high internal consistency and three subscales which were significantly associated with less involvement with alcohol use, cigarette use, and violent behaviors. [ABSTRACT FROM AUTHOR]

Published
2002
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45. AHA scientific statement. Cardiovascular health in childhood: a statement for health professionals from the Committee on Atherosclerosis, Hypertension, and Obesity in the Young (AHOY) of the Council on Cardiovascular Disease in the Young, American Heart Association [corrected] [published erratum appears in CIRCULATION 2002 Aug 27;106(9):1178].

Author

Williams CL, Hayman LL, Daniels SR, Robinson TN, Steinberger J, Paridon S, Bazzarre T, American Heart Association. Council on Cardiovascular Disease in the Young. Committee on Atherosclerosis Hypertension, and Obesity in the Young (AHOY), Williams, Christine L, Hayman, Laura L, Daniels, Stephen R, Robinson, Thomas N, Steinberger, Julia, Paridon, Stephen, and Bazzarre, Terry

Published
2002

46. Conversation intervention with Alzheimer's patients: increasing the relevance of communication.

Author

Tappen RM, Williams CL, Barry C, and DiSesa D

Abstract

The effectiveness of conversation in improving verbal communication of nursing home residents with Alzheimer's disease was compared to exercise and a combination of both interventions. Fifty-five participants were randomly assigned to treatment group and raters were blinded. Treatment was given three times weekly for 30 minutes, for 16 weeks. Although all groups evidenced decline in the total number of words used as a group, the conversation-only subjects' performance was significantly better in terms of the number of nonredundant units of information produced (p = .0433) and conciseness (p = .0101) using analysis of covariance controlling for baseline performance. Individual subjects' change in performance was also examined. Active engagement in structured one-on-one conversation may improve relevance of communication in this population. [ABSTRACT FROM AUTHOR]

Published
2002
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47. Efficacy and safety of lovastatin in adolescent males with heterozygous familial hypercholesterolemia: a randomized controlled trial.

Author

Stein EA, Illingworth DR, Kwiterovich PO Jr., Liacouras CA, Siimes MA, Jacobson MS, Brewster TG, Hopkins P, Davidson M, Graham K, Arensman F, Knopp RH, DuJovne C, Williams CL, Isaacsohn JL, Jacobsen CA, Laskarzewski PM, Ames S, Gormley GJ, and Stein, E A

Abstract

Context: Heterozygous familial hypercholesterolemia (HeFH) is a common disorder associated with early coronary artery disease, especially in men. The age at which drug therapy should be started is still controversial, as is the use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins).Objective: To assess the lipid-lowering efficacy, biochemical safety, and effect on growth and sexual development of lovastatin in adolescent boys with HeFH.Design: One-year, double-blind, placebo-controlled, balanced, 2-period, 2-arm randomized trial. In the first period (24 weeks), lovastatin was increased at 8 and 16 weeks and the dosage remained stable during the second period (24 weeks). The study was conducted between 1990 and 1994.Setting: Fourteen pediatric outpatient clinics in the United States and Finland.Patients: Boys aged 10 to 17 years with HeFH. Of 132 randomized subjects (67 intervention, 65 placebo), 122 (63 intervention, 59 placebo) and 110 (61 intervention, 49 placebo) completed the first and second periods, respectively.Intervention: Lovastatin, starting at 10 mg/d, with a forced titration at 8 and 16 weeks to 20 and 40 mg/d, respectively, or placebo.Main Outcome Measures: The primary efficacy outcome measure was low-density lipoprotein cholesterol (LDL-C). Primary safety measures were growth and sexual development.Results: Compared with placebo, LDL-C levels of patients receiving lovastatin decreased significantly (P<.001) by 17%, 24%, and 27% receiving dosages of 10, 20, and 40 mg/d, respectively, and remained 25 % lower than baseline at 48 weeks. Growth and sexual maturation assessed by Tanner staging and testicular volume were not significantly different between the lovastatin and placebo groups at 24 weeks (P = .85) and 48 weeks (P = .33); neither were serum hormone levels or biochemical parameters of nutrition. However, the study was underpowered to detect significant differences in safety parameters. Serum vitamin E levels were reduced with lovastatin treatment consistent with reductions in LDL-C, the major carrier of vitamin E in the circulation.Conclusions: This study in adolescent boys with HeFH confirmed the LDL-C-reducing effectiveness of lovastatin. Comprehensive clinical and biochemical data on growth, hormonal, and nutritional status indicated no significant differences between lovastatin and placebo over 48 weeks, although further study is required. [ABSTRACT FROM AUTHOR]

Published
1999
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48. The relationship between adolescent alcohol use and delinquent and violent behaviors.

Author

Komro KA, Williams CL, Forster JL, Perry CL, Farbakhsh K, and Stigler MH

Abstract

Longitudinal and cross-sectional relationships between alcohol use, psychological risk (as measured by four MMPI-A scales), and delinquent and violent behaviors were analyzed using self-reported data from eighth and ninth grade students from a rural and small town population. Alcohol use and acknowledgement of alcohol and drug-related problems were statistically associated with delinquent and violent behaviors, even after adjusting for personality and behavioral risk. These results suggest that alcohol use is an independent risk factor for delinquent and violent behaviors among young people. Violence prevention efforts among adolescents, therefore, should recognize and address alcohol use. Alcohol use prevention efforts among adolescents should evaluate the effects of reducing alcohol use on subsequent violent behaviors. [ABSTRACT FROM AUTHOR]

Published
1999

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