237 results on '"Corey, Brian."'
Search Results
2. Folksonomies in Crowdsourcing Platforms: Three Tensions Associated with the Development of Shared Language in Distributed Groups.
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Julia Bullard, Kevin Crowston, Corey Brian Jackson, Alexander Owen Smith, and Carsten S. østerlund
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- 2024
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3. Design Principles for Background Knowledge to Enhance Learning in Citizen Science.
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Kevin Crowston, Corey Brian Jackson, Isabella Corieri, and Carsten S. østerlund
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- 2023
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4. Assessing the Value Orientations of Contributors to Virtual Citizen Science Projects.
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Eunmi (Ellie) Jeong, Corey Brian Jackson, Liz Dowthwaite, Tallal Ahmad, and Laura Trouille
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- 2023
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5. Wavelet-Based Characterization of Small-Scale Solar Emission Features at Low Radio Frequencies
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Suresh, Akshay, Sharma, Rohit, Oberoi, Divya, Das, Srijan B., Pankratius, Victor, Timar, Brian, Lonsdale, Colin J., Bowman, Judd D., Briggs, Frank, Cappallo, Roger J., Corey, Brian E., Deshpande, Avinash A., Emrich, David, Goeke, Robert, Greenhill, Lincoln J., Hazelton, Bryna J., Johnston-Hollitt, Melanie, Kaplan, David L., Kasper, Justin C., Kratzenberg, Eric, Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward, Ord, Stephen M., Prabu, Thiagaraj, Rogers, Alan E. E., Roshi, Anish, Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, Ravi, Tingay, Steven J., Waterson, Mark, Wayth, Randall B., Webster, Rachel L., Whitney, Alan R., Williams, Andrew, and Williams, Christopher L.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
Low radio frequency solar observations using the Murchison Widefield Array have recently revealed the presence of numerous weak, short-lived and narrow-band emission features, even during moderately quiet solar conditions. These non-thermal features occur at rates of many thousands per hour in the 30.72 MHz observing bandwidth, and hence, necessarily require an automated approach for their detection and characterization. Here, we employ continuous wavelet transform using a mother Ricker wavelet for feature detection from the dynamic spectrum. We establish the efficacy of this approach and present the first statistically robust characterization of the properties of these features. In particular, we examine distributions of their peak flux densities, spectral spans, temporal spans and peak frequencies. We can reliably detect features weaker than 1 SFU, making them, to the best of our knowledge, the weakest bursts reported in literature. The distribution of their peak flux densities follows a power law with an index of -2.23 in the 12-155 SFU range, implying that they can provide an energetically significant contribution to coronal and chromospheric heating. These features typically last for 1-2 seconds and possess bandwidths of about 4-5 MHz. Their occurrence rate remains fairly flat in the 140-210 MHz frequency range. At the time resolution of the data, they appear as stationary bursts, exhibiting no perceptible frequency drift. These features also appear to ride on a broadband background continuum, hinting at the likelihood of them being weak type-I bursts., Comment: 15 pages, 14 figures, Accepted for publication in ApJ
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- 2016
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6. The Genie in the Bottle: Different Stakeholders, Different Interpretations of Machine Learning.
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Mahboobeh Harandi, Kevin Crowston, Corey Brian Jackson, and Carsten S. østerlund
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- 2020
7. A Digital-Receiver for the Murchison Widefield Array
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Prabu, Thiagaraj, Srivani, K. S., Roshi, D. Anish, Kamini, P. A., Madhavi, S., Emrich, David, Crosse, Brian, Williams, Andrew J., Waterson, Mark, Deshpande, Avinash A., Shankar, N. Udaya, Subrahmanyan, Ravi, Briggs, Frank H., Goeke, Robert F., Tingay, Steven J., Johnston-Hollitt, Melanie, R, Gopalakrishna M, Morgan, Edward H., Pathikulangara, Joseph, Bunton, John D., Hampson, Grant, Williams, Christopher, Ord, Stephen M., Wayth, Randall B., Kumar, Deepak, Morales, Miguel F., deSouza, Ludi, Kratzenberg, Eric, Pallot, D., McWhirter, Russell, Hazelton, Bryna J., Arcus, Wayne, Barnes, David G., Bernardi, Gianni, Booler, T., Bowman, Judd D., Cappallo, Roger J., Corey, Brian E., Greenhill, Lincoln J., Herne, David, Hewitt, Jacqueline N., Kaplan, David L., Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Lonsdale, Colin J., Lynch, Mervyn J., Mitchell, Daniel A., Oberoi, Divya, Remillard, Ronald A., Rogers, Alan E., Salah, Joseph E., Sault, Robert J., Stevens, Jamie B., Tremblay, S. E., Webster, Rachel L., Whitney, Alan R., and Wyithe, Stuart B.
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Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
An FPGA-based digital-receiver has been developed for a low-frequency imaging radio interferometer, the Murchison Widefield Array (MWA). The MWA, located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, consists of 128 dual-polarized aperture-array elements (tiles) operating between 80 and 300\,MHz, with a total processed bandwidth of 30.72 MHz for each polarization. Radio-frequency signals from the tiles are amplified and band limited using analog signal conditioning units; sampled and channelized by digital-receivers. The signals from eight tiles are processed by a single digital-receiver, thus requiring 16 digital-receivers for the MWA. The main function of the digital-receivers is to digitize the broad-band signals from each tile, channelize them to form the sky-band, and transport it through optical fibers to a centrally located correlator for further processing. The digital-receiver firmware also implements functions to measure the signal power, perform power equalization across the band, detect interference-like events, and invoke diagnostic modes. The digital-receiver is controlled by high-level programs running on a single-board-computer. This paper presents the digital-receiver design, implementation, current status, and plans for future enhancements., Comment: 14 pages, 7 figures
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- 2015
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8. Serendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array
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Hurley-Walker, Natasha, Johnston-Hollitt, Melanie, Ekers, Ron, Hunstead, Richard, Sadler, Elaine M., Hindson, Luke, Hancock, Paul, Bernardi, Gianni, Bowman, Judd D., Briggs, Frank, Cappallo, Roger, Corey, Brian, Deshpande, Avinash A., Emrich, David, Gaensler, Bryan M., Goeke, Robert, Greenhill, Lincoln, Hazelton, Bryna J., Hewitt, Jacqueline, Kaplan, David L., Kasper, Justin, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, Mitchell, Daniel, McWhirter, Russell, Morales, Miguel, Morgan, Edward, Oberoi, Divya, Offringa, Andre, Ord, Stephen, Prabu, Thiagaraj, Rogers, Alan, Roshi, Anish, Shankar, Udaya, Srivani, K., Subrahmanyan, Ravi, Tingay, Steven, Waterson, Mark, Wayth, Randall B., Webster, Rachel, Whitney, Alan, Williams, Andrew, and Williams, Chris
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Astrophysics - Astrophysics of Galaxies - Abstract
Recent observations with the Murchison Widefield Array at 185~MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby ($z = 0.0178$) radio galaxy associated with NGC\,1534. The diffuse emission presented here is the first indication that NGC\,1534 is one of a rare class of objects (along with NGC\,5128 and NGC\,612) in which a galaxy with a prominent dust lane hosts radio emission on scales of $\sim$700\,kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with disks. NGC1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2\,mJy\,arcmin$^{-2}$. The radio lobes have one of the steepest spectral indices yet observed: $\alpha=-2.1\pm0.1$, and the core to lobe luminosity ratio is $<0.1$\%. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as $7\times10^{-7}$\,Mpc$^{-3}$ and argue that normal AGN cannot spend more than 6\% of their lifetime in this phase if they all go through the same cycle., Comment: 12 pages, 7 figures, accepted MNRAS
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- 2014
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9. Shifting forms of Engagement: Volunteer Learning in Online Citizen Science.
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Corey Brian Jackson, Carsten S. østerlund, Kevin Crowston, Mahboobeh Harandi, and Laura Trouille
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- 2020
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10. Knowledge Tracing to Model Learning in Online Citizen Science Projects.
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Kevin Crowston, Shane L. Larson, Neda Rohani, Joshua R. Smith 0003, Laura Trouille, Michael Zevin, Carsten S. østerlund, Tae Kyoung Lee, Corey Brian Jackson, Mahboobeh Harandi, Sarah Allen, Sara Bahaadini, Scott Coughlin, and Aggelos K. Katsaggelos
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- 2020
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11. The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14,110 Compact Radio Sources over 6,100 Square Degrees
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Hurley-Walker, Natasha, Morgan, John, Wayth, Randall B., Hancock, Paul J., Bell, Martin E., Bernardi, Gianni, Bhat, Ramesh, Briggs, Frank, Deshpande, Avinash A., Ewall-Wice, Aaron, Feng, Lu, Hazelton, Bryna J., Hindson, Luke, Jacobs, Daniel C., Kudryavtseva, David L. Kaplan Nadia, Lenc, Emil, McKinley, Benjamin, Mitchell, Daniel, Pindor, Bart, Procopio, Pietro, Oberoi, Divya, Offringa, André, Ord, Stephen, Riding, Jennifer, Bowman, Judd D., Cappallo, Roger, Corey, Brian, Emrich, David, Gaensler, B. M., Goeke, Robert, Greenhill, Lincoln, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kasper, Justin, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, Russell, Morales, Miguel F., Morgan, Edward, Prabu, Thiagaraj, Rogers, Alan, Roshi, Anish, Shankar, Udaya, Srivani, K., Subrahmanyan, Ravi, Tingay, Steven, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, and Williams, Chris
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Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
We present the results of an approximately 6,100 square degree 104--196MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the Murchison Widefield Array Commissioning Survey (MWACS). The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h < Right Ascension (RA) < 8.5 h, -58 deg < Declination (Dec) < -14 deg over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6--3 arcmin. The catalogue has 3-arcmin angular resolution and a typical noise level of 40 mJy/beam, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaiced snapshots, flux density calibration and source-finding method. We present a catalogue of flux density and spectral index measurements for 14,110 sources, extracted from the mosaic, 1,247 of which are sub-components of complexes of sources., Comment: 22 pages, 18 figures, accepted to PASA
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- 2014
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12. The low-frequency characteristics of PSR J0437-4715 observed with the Murchison Widefield Array
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Bhat, N. D. Ramesh, Ord, S. M., Tremblay, S. E., Tingay, S. J., Deshpande, Avinash, van Straten, W., Oronsaye, S., Bernardi, G., Bowman, Judd, Briggs, F., Cappallo, R. J., Corey, Brian, Emerich, D., Goeke, R, Greenhill, Lincoln, Hazelton, Bryna, Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kaplan, David, Kasper, Justin, Kratzenberg, E., Lonsdale, C. J., Lynch, M. J., McWhirter, S., Mitchell, D. A., Morales, Miguel, Morgan, Edward H., Oberoi, Divya, Prabu, Thayagaraja, Rogers, Alan E. E., Roshi, D. A., Udayashankar, N., Srivani, K. S., Subramanyan, R., Waterson, M., Wayth, Randall, Webster, Rachel, Whitney, Alan, Williams, A., and Wiliams, C. L.
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Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
We report on the detection of the millisecond pulsar PSR J0437-4715 with the Murchison Widefield Array (MWA) at a frequency of 192 MHz. Our observations show rapid modulations of pulse intensity in time and frequency that arise from diffractive scintillation effects in the interstellar medium (ISM), as well as prominent drifts of intensity maxima in the time-frequency plane that arise from refractive effects. Our analysis suggests that the scattering screen is located at a distance of $\sim$80-120 pc from the Sun, in disagreement with a recent claim that the screen is closer ($\sim$10 pc). Comparisons with higher frequency data from Parkes reveals a dramatic evolution of the pulse profile with frequency, with the outer conal emission becoming comparable in strength to that from the core and inner conal regions. As well as demonstrating high time resolution science capabilities currently possible with the MWA, our observations underscore the potential to conduct low-frequency investigations of timing-array millisecond pulsars, which may lead to increased sensitivity for the detection of nanoHertz gravitational waves via the accurate characterisation of ISM effects., Comment: 6 pages, 4 figures, 1 table, Accepted for publication in ApJ Letters
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- 2014
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13. Study of Redshifted HI from the Epoch of Reionization with Drift scan
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Paul, Sourabh, Sethi, Shiv K., Subrahmanyan, Ravi, Shankar, N. Udaya, Dwarakanath, K. S., Deshpande, Avinash A., Bernardi, Gianni, Bowman, Judd D., Briggs, Frank, Cappallo, Roger J., Corey, Brian E., Emrich, David, Gaensler, Bryan M., Goeke, Robert F., Greenhill, Lincoln J., Hazelton, Bryna J., Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kaplan, David L., Kasper, Justin C., Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward H., Oberoi, Divya, Ord, Stephen M., Prabu, Thiagaraj, Rogers, Alan E. E., Roshi, Anish A., Srivani, K. S., Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., and Williams, Christopher L.
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Astrophysics - Instrumentation and Methods for Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics - 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., Comment: 23 pages, 14 figures, accepted for publication in ApJ
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- 2014
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14. A study of fundamental limitations to statistical detection of redshifted HI from the epoch of reionization
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Thyagarajan, Nithyanandan, Shankar, N. Udaya, Subrahmanyan, Ravi, Arcus, Wayne, Bernardi, Gianni, Bowman, Judd D., Briggs, Frank, Bunton, John D., Cappallo, Roger J., Corey, Brian E., deSouza, Ludi, Emrich, David, Gaensler, Bryan M., Goeke, Robert F., Greenhill, Lincoln J., Hazelton, Bryna J., Herne, David, Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kaplan, David L., Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward H., Oberoi, Divya, Ord, Stephen M., Pathikulangara, Joseph, Remillard, Ronald A., Rogers, Alan E. E., Roshi, Anish A., Salah, Joseph E., Sault, Robert J., Srivani, K. S., Stevens, Jamie B., Thiagaraj, Prabu, Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., Williams, Christopher L., and Wyithe, J. Stuart B.
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Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
In this paper we explore for the first time the relative magnitudes of three fundamental sources of uncertainty, namely, foreground contamination, thermal noise and sample variance in detecting the HI power spectrum from the Epoch of Reionization (EoR). We derive limits on the sensitivity of a Fourier synthesis telescope to detect EoR based on its array configuration and a statistical representation of images made by the instrument. We use the Murchison Widefield Array (MWA) configuration for our studies. Using a unified framework for estimating signal and noise components in the HI power spectrum, we derive an expression for and estimate the contamination from extragalactic point-like sources in three-dimensional k-space. Sensitivity for EoR HI power spectrum detection is estimated for different observing modes with MWA. With 1000 hours of observing on a single field using the 128-tile MWA, EoR detection is feasible (S/N > 1 for $k\lesssim 0.8$ Mpc$^{-1}$). Bandpass shaping and refinements to the EoR window are found to be effective in containing foreground contamination, which makes the instrument tolerant to imaging errors. We find that for a given observing time, observing many independent fields of view does not offer an advantage over a single field observation when thermal noise dominates over other uncertainties in the derived power spectrum., Comment: 19 pages, 14 figures (19 figures in total including subfigures), 2 appendices, in press for publication in ApJ
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- 2013
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15. Talking the Talk in Citizen Science.
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Mahboobeh Harandi, Corey Brian Jackson, Carsten S. østerlund, and Kevin Crowston
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- 2018
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16. Science with the Murchison Widefield Array
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Bowman, Judd D., Cairns, Iver, Kaplan, David L., Murphy, Tara, Oberoi, Divya, Staveley-Smith, Lister, Arcus, Wayne, Barnes, David G., Bernardi, Gianni, Briggs, Frank H., Brown, Shea, Bunton, John D., Burgasser, Adam J., Cappallo, Roger J., Chatterjee, Shami, Corey, Brian E., Coster, Anthea, Deshpande, Avinash, deSouza, Ludi, Emrich, David, Erickson, Philip, Goeke, Robert F., Gaensler, B. M., Greenhill, Lincoln J., Harvey-Smith, Lisa, Hazelton, Bryna J., Herne, David, Hewitt, Jacqueline N., Johnston-Hollitt, Melanie, Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., Matthews, Lynn D., McWhirter, S. Russell, Mitchell, Daniel A., Morales, Miguel F., Morgan, Edward H., Ord, Stephen M., Pathikulangara, Joseph, Thiagaraj, Prabu, Remillard, Ronald A., Robishaw, Timothy, Rogers, Alan E. E., Roshi, Anish A., Salah, Joseph E., Sault, Robert J., Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie B., Subrahmanyan, Ravi, Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., Williams, Christopher L., and Wyithe, J. Stuart B.
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Astrophysics - Instrumentation and Methods for Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Astrophysics - Solar and Stellar Astrophysics - Abstract
Significant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the Southern Hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21 cm emission from the epoch of reionisation in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives., Comment: Updated with revisions. 32 pages including figures and references. Submitted to PASA
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- 2012
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17. Demonstration of a broadband-RF VLBI system at 16 Gbps data rate per station
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Whitney, Alan R., Beaudoin, Christopher J., Cappallo, Roger J., Corey, Brian E., Crew, Geoffrey B., Doeleman, Shepherd S., Lapsley, David E., Hinton, Alan A., McWhirter, Stephen R., Niell, Arthur E., Rogers, Alan E. E., Ruszczyk, Chester A., Smythe, Daniel L., SooHoo, Jason, and Titus, Michael A.
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Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
The recent development of a relatively inexpensive 16-Gbps data-recording system based on commercial off-the-shelf technology and open-source software, along with parallel development in broadband Very Long Baseline Interferometry (VLBI) techniques, is enabling dramatically improved sensitivity for both astronomical and geodetic VLBI. The system is described, including the results of a demonstration VLBI experiment that illustrates a number of cutting-edge technologies that can be deployed in the near future to significantly enhance the power of the VLBI technique., Comment: Submitted to PASP
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- 2012
18. Fast Holographic Deconvolution: a new technique for precision radio interferometry
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Sullivan, Ian, Morales, Miguel, Hazelton, Bryna, Arcus, Wayne, Barnes, David, Bernardi, Gianni, Briggs, Frank, Bowman, Judd D., Bunton, John, Cappallo, Roger, Corey, Brian, Deshpande, Avinash, deSouza, Ludi, Emrich, David, Gaensler, B. M., Goeke, Robert, Greenhill, Lincoln, Herne, David, Hewitt, Jacqueline, Johnston-Hollitt, Melanie, Kaplan, David, Kasper, Justin, Kincaid, Barton, Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin, Lynch, Mervyn, McWhirter, Russell, Mitchell, Daniel, Morgan, Edward, Oberoi, Divya, Ord, Stephen, Pathikulangara, Joseph, Prabu, Thiagaraj, Remillard, Ron, Rogers, Alan, Roshi, Anish, Salah, Joseph, Sault, Robert, Shankar, Udaya, Srivani, K., Stevens, Jamie, Subrahmanyan, Ravi, Tingay, Steven, Wayth, Randall, Waterson, Mark, Webster, Rachel, Whitney, Alan, Williams, Andrew, Williams, Chris, and Wyithe, Stuart
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Astrophysics - Instrumentation and Methods for Astrophysics ,Astrophysics - Cosmology and Extragalactic Astrophysics - Abstract
We introduce the Fast Holographic Deconvolution method for analyzing interferometric radio data. Our new method is an extension of A-projection/software-holography/forward modeling analysis techniques and shares their precision deconvolution and widefield polarimetry, while being significantly faster than current implementations that use full direction-dependent antenna gains. Using data from the MWA 32 antenna prototype, we demonstrate the effectiveness and precision of our new algorithm. Fast Holographic Deconvolution may be particularly important for upcoming 21 cm cosmology observations of the Epoch of Reionization and Dark Energy where foreground subtraction is intimately related to the precision of the data reduction., Comment: ApJ accepted
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- 2012
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19. Low Frequency Imaging of Fields at High Galactic Latitude with the Murchison Widefield Array 32-Element Prototype
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Williams, Christopher L., Hewitt, Jacqueline N., Levine, Alan M., de Oliveira-Costa, Angelica, Bowman, Judd D., Briggs, Frank H., Gaensler, B. M., Hernquist, Lars L., Mitchell, Daniel A., Morales, Miguel F., Sethi, Shiv K., Subrahmanyan, Ravi, Sadler, Elaine M., Arcus, Wayne, Barnes, David G., Bernardi, Gianni, Bunton, John D., Cappallo, Roger C., Crosse, Brian W., Corey, Brian E., Deshpande, Avinash, deSouza, Ludi, Emrich, David, Goeke, Robert F., Greenhill, Lincoln J., Hazelton, Bryna J., Herne, David, Kaplan, David L., Kasper, Justin C., Kincaid, Barton B., Koenig, Ronald, Kratzenberg, Eric, Lonsdale, Colin J., Lynch, Mervyn J., McWhirter, S. Russell, Mitchell, %Daniel A., Morales, %Miguel F., Morgan, Edward H., Oberoi, Divya, Ord, Stephen M., Pathikulangara, Joseph, Prabu, Thiagaraj, Remillard, Ronald A., Rogers, Alan E. E., Roshi, Anish A., Salah, Joseph E., Sault, Robert J., Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie B., Tingay, Steven J., Wayth, Randall B., Waterson, Mark, Webster, Rachel L., Whitney, Alan R., Williams, Andrew J., and Wyithe, J. Stuart B.
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Astrophysics - Cosmology and Nongalactic Astrophysics ,Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
The Murchison Widefield Array (MWA) is a new low-frequency, wide field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. We have used a 32-element MWA prototype interferometer (MWA-32T) to observe two 50-degree diameter fields in the southern sky in the 110 MHz to 200 MHz band in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce ~15' angular resolution maps of the two fields. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110 MHz to 200 MHz band., Comment: 20 pages, 6 tables, 12 figures. 1 online-only machine readable table. Submitted to ApJ
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- 2012
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20. First Spectroscopic Imaging Observations of the Sun at Low Radio Frequencies with the Murchison Widefield Array Prototype
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Oberoi, Divya, Matthews, Lynn D., Cairns, Iver H., Emrich, David, Lobzin, Vasili, Lonsdale, Colin J., Morgan, Edward H., Prabu, T., Vedantham, Harish, Wayth, Randall B., Williams, Andrew, Williams, Christopher, White, Stephen M., Allen, G., Arcus, Wayne, Barnes, David, Benkevitch, Leonid, Bernardi, Gianni, Bowman, Judd D., Briggs, Frank H., Bunton, John D., Burns, Steve, Cappallo, Roger C., Clark, M. A., Corey, Brian E., Dawson, M., DeBoer, David, De Gans, A., deSouza, Ludi, Derome, Mark, Edgar, R. G., Elton, T., Goeke, Robert, Gopalakrishna, M. R., Greenhill, Lincoln J., Hazelton, Bryna, Herne, David, Hewitt, Jacqueline N., Kamini, P. A., Kaplan, David L., Kasper, Justin C., Kennedy, Rachel, Kincaid, Barton B., Kocz, Jonathan, Koeing, R., Kowald, Errol, Lynch, Mervyn J., Madhavi, S., McWhirter, Stephen R., Mitchell, Daniel A., Morales, Miguel F., Ng, A., Ord, Stephen M., Pathikulangara, Joseph, Rogers, Alan E. E., Roshi, Anish, Salah, Joseph E., Sault, Robert J., Schinckel, Antony, Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie, Subrahmanyan, Ravi, Thakkar, D., Tingay, Steven J., Tuthill, J., Vaccarella, Annino, Waterson, Mark, Webster, Rachel L., and Whitney, Alan R.
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Astrophysics - Solar and Stellar Astrophysics - Abstract
We present the first spectroscopic images of solar radio transients from the prototype for the Murchison Widefield Array (MWA), observed on 2010 March 27. Our observations span the instantaneous frequency band 170.9-201.6 MHz. Though our observing period is characterized as a period of `low' to `medium' activity, one broadband emission feature and numerous short-lived, narrowband, non-thermal emission features are evident. Our data represent a significant advance in low radio frequency solar imaging, enabling us to follow the spatial, spectral, and temporal evolution of events simultaneously and in unprecedented detail. The rich variety of features seen here reaffirms the coronal diagnostic capability of low radio frequency emission and provides an early glimpse of the nature of radio observations that will become available as the next generation of low frequency radio interferometers come on-line over the next few years., Comment: 15 pages, 5 figures, accepted for publication in Astrophysical Journal Letters. Movies for figures 4 and 5 available at http://www.mwatelescope.org/info/mwa_proto.html
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- 2011
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21. The Murchison Widefield Array: Design Overview
- Author
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Lonsdale, Colin J., Cappallo, Roger J., Morales, Miguel F., Briggs, Frank H., Benkevitch, Leonid, Bowman, Judd D., Bunton, John D., Burns, Steven, Corey, Brian E., deSouza, Ludi, Doeleman, Sheperd S., Derome, Mark, Deshpande, Avinash, Gopalakrishna, M. R., Greenhill, Lincoln J., Herne, David, Hewitt, Jacqueline N., Kamini, P. A., Kasper, Justin C., Kincaid, Barton B., Kocz, Jonathan, Kowald, Errol, Kratzenberg, Eric, Kumar, Deepak, Lynch, Mervyn J., Madhavi, S., Matejek, Michael, Mitchell, Daniel, Morgan, Edward, Oberoi, Divya, Ord, Steven, Pathikulangara, Joseph, Prabu, T., Rogers, Alan E. E., Roshi, Anish, Salah, Joseph E., Sault, Robert J., Shankar, N. Udaya, Srivani, K. S., Stevens, Jamie, Tingay, Steven, Vaccarella, Annino, Waterson, Mark, Wayth, Randall B., Webster, Rachel L., Whitney, Alan R., Williams, Andrew, and Williams, Christopher
- Subjects
Astrophysics - Instrumentation and Methods for Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics ,Astrophysics - Solar and Stellar Astrophysics - Abstract
The Murchison Widefield Array (MWA) is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations, but is initially focused on three key science projects. These are detection and characterization of 3-dimensional brightness temperature fluctuations in the 21cm line of neutral hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10, solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources,and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broad-band active dipoles, arranged into 512 tiles comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5km in diameter, with a small number of outliers extending to 3km. All tile-tile baselines are correlated in custom FPGA-based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function (PSF) quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities., Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings of the IEEE
- Published
- 2009
- Full Text
- View/download PDF
22. Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
- Author
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Doeleman, Sheperd, Weintroub, Jonathan, Rogers, Alan E. E., Plambeck, Richard, Freund, Robert, Tilanus, Remo P. J., Friberg, Per, Ziurys, Lucy M., Moran, James M., Corey, Brian, Young, Ken H., Smythe, Daniel L., Titus, Michael, Marrone, Daniel P., Cappallo, Roger J., Bock, Douglas C. J., Bower, Geoffrey C., Chamberlin, Richard, Davis, Gary R., Krichbaum, Thomas P., Lamb, James, Maness, Holly, Niell, Arthur E., Roy, Alan, Strittmatter, Peter, Werthimer, Daniel, Whitney, Alan R., and Woody, David
- Subjects
Astrophysics - Abstract
The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation (ref 1). Sagittarius A*, the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4 million times that of the Sun (refs. 2,3). A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A* where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering (refs. 4-7). Here we report observations at a wavelength of 1.3 mm that set a size of 37 (+16, -10; 3-sigma) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of SgrA* emission may not be not centred on the black hole, but arises in the surrounding accretion flow., Comment: 12 pages including 2 figures
- Published
- 2008
- Full Text
- View/download PDF
23. Field Deployment of Prototype Antenna Tiles for the Mileura Widefield Array--Low Frequency Demonstrator
- Author
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Bowman, Judd D., Barnes, David G., Briggs, Frank H., Corey, Brian E., Lynch, Merv J., Bhat, N. D. Ramesh, Cappallo, Roger J., Doeleman, Sheperd S., Fanous, Brian J., Herne, David, Hewitt, Jacqueline N., Johnston, Chris, Kasper, Justin C., Kocz, Jonathon, Kratzenberg, Eric, Lonsdale, Colin J., Morales, Miguel F., Oberoi, Divya, Salah, Joseph E., Stansby, Bruce, Stevens, Jamie, Torr, Glen, Wayth, Randall, Webster, Rachel L., and Wyithe, J. Stuart B.
- Subjects
Astrophysics - Abstract
Experiments were performed with prototype antenna tiles for the Mileura Widefield Array--Low Frequency Demonstrator (MWA-LFD) to better understand the widefield, wideband properties of their design and to characterize the radio frequency interference (RFI) between 80 and 300 MHz at the site in Western Australia. Observations acquired during the six month deployment confirmed the predicted sensitivity of the antennas, sky-noise dominated system temperatures, and phase-coherent interferometric measurements. The radio spectrum is remarkably free of strong terrestrial signals, with the exception of two narrow frequency bands allocated to satellite downlinks and rare bursts due to ground-based transmissions being scattered from aircraft and meteor trails. Results indicate the potential of the MWA-LFD to make significant achievements in its three key science objectives: epoch of reionziation science, heliospheric science, and radio transient detection., Comment: Accepted by AJ. 17 pages with figures
- Published
- 2006
- Full Text
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24. Linguistic Changes in Online Citizen Science: A Structurational Perspective.
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Corey Brian Jackson, Carsten S. østerlund, Mahboobeh Harandi, Dhruv Kharwar, and Kevin Crowston
- Published
- 2019
25. Did they login?: Patterns of Anonymous Contributions in Online Communities.
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Corey Brian Jackson, Kevin Crowston, and Carsten S. østerlund
- Published
- 2018
- Full Text
- View/download PDF
26. Folksonomies to Support Coordination and Coordination of Folksonomies.
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Corey Brian Jackson, Kevin Crowston, Carsten S. østerlund, and Mahboobeh Harandi
- Published
- 2018
- Full Text
- View/download PDF
27. Addressing The Privacy Paradox through Personalized Privacy Notifications.
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Corey Brian Jackson and Yang Wang 0005
- Published
- 2018
- Full Text
- View/download PDF
28. Encouraging Work in Citizen Science: Experiments in Goal Setting and Anchoring.
- Author
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Corey Brian Jackson, Gabriel H. Mugar, Kevin Crowston, and Carsten S. østerlund
- Published
- 2016
- Full Text
- View/download PDF
29. Which Way Did They Go? Newcomer Movement through the Zooniverse.
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Corey Brian Jackson, Carsten S. østerlund, Veronica Maidel, Kevin Crowston, and Gabriel H. Mugar
- Published
- 2016
- Full Text
- View/download PDF
30. 'Guess what! You're the First to See this Event': Increasing Contribution to Online Production Communities.
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Corey Brian Jackson, Kevin Crowston, Gabriel H. Mugar, and Carsten S. østerlund
- Published
- 2016
- Full Text
- View/download PDF
31. Motivations for Sustained Participation in Crowdsourcing: Case Studies of Citizen Science on the Role of Talk.
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Corey Brian Jackson, Carsten S. østerlund, Gabriel H. Mugar, Katie DeVries Hassman, and Kevin Crowston
- Published
- 2015
- Full Text
- View/download PDF
32. Being present in online communities: learning in citizen science.
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Gabriel H. Mugar, Carsten S. østerlund, Corey Brian Jackson, and Kevin Crowston
- Published
- 2015
- Full Text
- View/download PDF
33. Planet hunters and seafloor explorers: legitimate peripheral participation through practice proxies in online citizen science.
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Gabriel H. Mugar, Carsten S. østerlund, Katie DeVries Hassman, Kevin Crowston, and Corey Brian Jackson
- Published
- 2014
- Full Text
- View/download PDF
34. Building an Apparatus: Refractive, Reflective, and Diffractive Readings of Trace Data.
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Carsten S. østerlund, Kevin Crowston, and Corey Brian Jackson
- Published
- 2020
35. Teaching citizen scientists to categorize glitches using machine learning guided training.
- Author
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Corey Brian Jackson, Carsten S. østerlund, Kevin Crowston, Mahboobeh Harandi, Sarah Allen, Sara Bahaadini, Scotty Coughlin, Vicky Kalogera, Aggelos K. Katsaggelos, Shane L. Larson, Neda Rohani, Joshua R. Smith 0003, Laura Trouille, and Michael Zevin
- Published
- 2020
- Full Text
- View/download PDF
36. Face-to-Face Matters: Inspirations from the Human Library.
- Author
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Corey Brian Jackson, Yun Huang, and Abby S. Kasowitz-Scheer
- Published
- 2015
- Full Text
- View/download PDF
37. Demonstration of a 16 Gbps Station -1 Broadband-RF VLBI System
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Whitney, Alan R., Beaudoin, Christopher J., Cappallo, Roger J., Corey, Brian E., Crew, Geoffrey B., Doeleman, Shepherd S., Lapsley, David E., Hinton, Alan A., McWhirter, Stephen R., Niell, Arthur E., Rogers, Alan E. E., Ruszczyk, Chester A., Smythe, Daniel L., SooHoo, Jason, and Titus, Michael A.
- Published
- 2013
- Full Text
- View/download PDF
38. Earth Orientation Parameter Estimates from Geodetic VLBI observations in the ITRF2020
- Author
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Mondal, Dhiman, Elosegui, Pedro, Barrett, John, Corey, Brian E., Niell, Arthur E., Ruszczyk, Chester A., Titus, Michael A., Mondal, Dhiman, Elosegui, Pedro, Barrett, John, Corey, Brian E., Niell, Arthur E., Ruszczyk, Chester A., and Titus, Michael A.
- Abstract
The International Terrestrial Reference Frame (ITRF) provides a framework for all ground- and space-based measurements that help determine locations on the Earth's surface with high precision. ITRF is realized every few years using the four space geodetic techniques, VLBI, GNSS, SLR, and DORIS. The most recent release, ITRF2020, is expected to be more precise than its predecessor, ITRF2014, which was released in 2016. For the first time, this realization of ITRF includes geodetic products from VLBI Global Observing Systems (VGOS), the next-generation broadband VLBI observing system equipped with fast antennas and wide observing bandwidths. By design, the uncertainties of VGOS observations are significantly smaller than those of its predecessor, the S/X Legacy system. With the inclusion of VGOS observations in ITRF2020, the VGOS network should be compatible and aligned with the S/X Legacy network and other space geodetic techniques. Therefore, one would expect the Earth Orientation Parameters (EOP) estimated from VGOS and S/X Legacy networks to be in good agreement. In this presentation, we will investigate the level of agreement of EOPs estimates from both networks in the ITRF2020, and also in relation to prior realizations such as ITRF2014
- Published
- 2022
39. Shifting forms of Engagement: Volunteer Learning in Online Citizen Science
- Author
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Carsten Østerlund, Mahboobeh Harandi, Corey Brian Jackson, Kevin Crowston, and Laura Trouille
- Subjects
Scope (project management) ,Computer Networks and Communications ,business.industry ,05 social sciences ,02 engineering and technology ,Public relations ,Peer production ,Human-Computer Interaction ,Discussion board ,Outcome variable ,020204 information systems ,0202 electrical engineering, electronic engineering, information engineering ,Citizen science ,0501 psychology and cognitive sciences ,Data recording ,Psychology ,business ,050107 human factors ,Social Sciences (miscellaneous) ,TRACE (psycholinguistics) - Abstract
Peer production projects involve people in many tasks, from editing articles to analyzing datasets. To facilitate mastery of these practices, projects offer a number of learning resources, ranging from project-defined FAQsto individually-oriented search tools and communal discussion boards. However, it is not clear which project resources best support participant learning, overall and at different stages of engagement. We draw onSørensen's framework of forms of presence to distinguish three types of engagement with learning resources:authoritative, agent-centered and communal. We assigned resources from the Gravity Spy citizen-science into these three categories and analyzed trace data recording interactions with resources using a mixed-effects logistic regression with volunteer performance as an outcome variable. The findings suggest that engagement with authoritative resources (e.g., those constructed by project organizers) facilitates performance initially. However, as tasks become more difficult, volunteers seek and benefit from engagement with their own agent-centered resources and community-generated resources. These findings suggest a broader scope for the design of learning resources for peer production
- Published
- 2020
40. Building an Apparatus: Refractive, Reflective, and Diffractive Readings of Trace Data
- Author
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Corey Brian Jackson, Carsten Østerlund, and Kevin Crowston
- Subjects
Trace (semiology) ,Optics ,business.industry ,Computer science ,business ,Computer Science Applications ,Information Systems - Published
- 2020
41. Discovering features in gravitational-wave data through detector characterization, citizen science and machine learning
- Author
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Kevin Crowston, O. Patane, R. R. Rote, Aggelos K. Katsaggelos, M. A.Lobato Rodriguez, S. B. Coughlin, S. Soni, W. F. Domainko, K. Kaminski, B. Téglás, Chengzhi Zhang, Mahboobeh Harandi, Carsten Østerlund, Laura Trouille, P. Nauta, U. Marciniak, C. Unsworth, V. G. Baranowski, Corey Brian Jackson, G. Niklasch, and Christopher P. L. Berry
- Subjects
Physics ,Physics - Instrumentation and Detectors ,Physics and Astronomy (miscellaneous) ,Artificial neural network ,010308 nuclear & particles physics ,Gravitational wave ,Scattering ,Astrophysics::High Energy Astrophysical Phenomena ,Detector ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,General Relativity and Quantum Cosmology (gr-qc) ,Instrumentation and Detectors (physics.ins-det) ,01 natural sciences ,LIGO ,General Relativity and Quantum Cosmology ,Glitch ,Transient noise ,0103 physical sciences ,State (computer science) ,Astrophysics - Instrumentation and Methods for Astrophysics ,010303 astronomy & astrophysics ,Algorithm ,Instrumentation and Methods for Astrophysics (astro-ph.IM) - Abstract
The observation of gravitational waves is hindered by the presence of transient noise (glitches). We study data from the third observing run of the Advanced LIGO detectors, and identify new glitch classes. Using training sets assembled by monitoring of the state of the detector, and by citizen-science volunteers, we update the Gravity Spy machine-learning algorithm for glitch classification. We find that a new glitch class linked to ground motion at the detector sites is especially prevalent, and identify two subclasses of this linked to different types of ground motion. Reclassification of data based on the updated model finds that 27 % of all transient noise at LIGO Livingston belongs to the new glitch class, making it the most frequent source of transient noise at that site. Our results demonstrate both how glitch classification can reveal potential improvements to gravitational-wave detectors, and how, given an appropriate framework, citizen-science volunteers may make discoveries in large data sets., 26 pages, 10 figures
- Published
- 2021
42. Did they login?
- Author
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Corey Brian Jackson, Carsten Østerlund, and Kevin Crowston
- Subjects
Computer Networks and Communications ,business.industry ,Computer science ,05 social sciences ,Internet privacy ,Support ,02 engineering and technology ,Login ,Human-Computer Interaction ,Unique identifier ,020204 information systems ,User identifier ,0202 electrical engineering, electronic engineering, information engineering ,Citizen science ,0501 psychology and cognitive sciences ,Empirical evidence ,business ,050107 human factors ,Social Sciences (miscellaneous) ,Anonymity - Abstract
Researchers studying user behaviors in online communities often conduct analyses of user interaction data recorded in system logs e.g., an edit in Wikipedia. Such analysis relies on collating interactions by a unique identifier such as a user ID. However, if users can contribute without being logged-in (i.e., anonymously) analysis of interaction data omit part of a user's experience. Problematically, anonymous traces are unlikely to be randomly distributed, so their omission can change statistical conclusions, with implications for both research and practice. To understand the impacts on conclusions of leaving out anonymous traces, we conducted an analysis of system logs from two online citizen science projects. Attributing anonymous traces with user IDs, we found that (1) many users contribute anonymously, though with varied patterns; and (2) attributing anonymous traces diminishes empirical evidence used to support theory and change the results of system algorithms. These results suggest anonymous traces have implications for research on user behaviors and the practices associated with using such data to tailor user experiences in online communities.
- Published
- 2018
43. Learning at the Seafloor, Looking at the Sky: The Relationship Between Individual Tasks and Collaborative Engagement in Two Citizen Science Projects.
- Author
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Katie DeVries Hassman, Gabriel H. Mugar, Carsten S. østerlund, and Corey Brian Jackson
- Published
- 2013
44. A first look at mixed VGOS-S/X correlation and post-processing
- Author
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Barrett, John, Cappallo, R.J., Corey, Brian E., Elosegui, Pedro, Mondal, Dhiman, Niell, Arthur E., Ruszczyk, Chester A., and Titus, Michael A.
- Abstract
25th European VLBI Group for Geodesy and Astronomy Working Meeting, 14-18 March 2021, The processing of geodetic VLBI experiments involving both S/X and VGOS stations is highly desirable for a multitude of reasons. Beyond the express purpose of obtaining geodetic ties between existing S/X stations and the rapidly expanding network of VGOS stations, a period of overlap and integration between the two systems is beneficial in order to help preserve reference frame continuity during the transition from the S/X to VGOS network, as well as to provide an opportunity to study any systematic differences between the two. Therefore, it is important to correlate and fringe-fit data collected contemporaneously by both S/X and VGOS stations to obtain delay observables on mixed baselines. A brief overview of one possible implementation of this process will be presented, describing correlation (including the use of the DiFX zoom-bands feature) along with the peculiarities of data handling on mixed S/X-VGOS baselines during post-processing with fourfit. Some results from the mixed-mode sessions RD2005 and RD2006 will be presented, and future prospects will be discussed
- Published
- 2021
45. A preliminary assessment of the accuracy of the VGOS geodetic products: implications for the terrestrial reference frame and Earth orientation parameters
- Author
-
Mondal, Dhiman, Elosegui, Pedro, Barrett, John, Corey, Brian E., Niell, Arthur E., Ruszczyk, Chester A., Titus, Michael A., Mondal, Dhiman, Elosegui, Pedro, Barrett, John, Corey, Brian E., Niell, Arthur E., Ruszczyk, Chester A., and Titus, Michael A.
- Abstract
The next-generation VLBI system called VGOS (VLBI Global Observing System) has been designed and built as a significant improvement over the legacy geodetic VLBI system to meet the accuracy and stability goals set by the Global Geodetic Observing System (GGOS). Improved geodetic products are expected as the VGOS technique transitions from demonstration to operational status, which is underway. Since 2019, a network of nine VGOS stations has been observing bi-weekly under the auspices of the International VLBI Service for Geodesy and Astrometry (IVS) to generate standard geodetic products. These products, together with the mixed-mode VLBI observations that tie the VGOS and legacy networks together will be contributions to the next realization of the International Terrestrial Reference Frame (ITRF2020). Moreover, since 2020 a subset of 2 to 4 VGOS stations has also been observing in a VLBI Intensive-like mode to assess the feasibility of Earth rotation (UT1) estimation using VGOS. Intensives are daily legacy VLBI observations that are run on a daily basis using a single baseline between Kokee Park Geophysical Observatory, Hawaii, and Wettzell Observatory, Germany, made with the goal of near-real-time monitoring of UT1. In this presentation, we will describe the VGOS observations, correlation, post-processing, and preliminary geodetic results, including UT1. We will also compare the VGOS estimates to estimates from legacy VLBI, including estimates from mixed-mode observations, to explore the precision and accuracy of the VGOS products
- Published
- 2021
46. VLBI measurement of the vector baseline between geodetic antennas at Kokee Park Geophysical Observatory, Hawaii
- Author
-
Agencia Estatal de Investigación (España), Niell, Arthur E., Barrett, John, Cappallo, R.J., Corey, Brian E., Elosegui, Pedro, Mondal, Dhiman, Rajagopalan, G., Ruszczyk, Chester A., Titus, Michael A., Agencia Estatal de Investigación (España), Niell, Arthur E., Barrett, John, Cappallo, R.J., Corey, Brian E., Elosegui, Pedro, Mondal, Dhiman, Rajagopalan, G., Ruszczyk, Chester A., and Titus, Michael A.
- Abstract
We measured the components of the 31-m-long vector between the two very-long-baseline interferometry (VLBI) antennas at the Kokee Park Geophysical Observatory (KPGO), Hawaii, with approximately 1 mm precision using phase delay observables from dedicated VLBI observations in 2016 and 2018. The two KPGO antennas are the 20 m legacy VLBI antenna and the 12 m VLBI Global Observing System (VGOS) antenna. Independent estimates of the vector between the two antennas were obtained by the National Geodetic Survey (NGS) using standard optical surveys in 2015 and 2018. The uncertainties of the latter survey were 0.3 and 0.7 mm in the horizontal and vertical components of the baseline, respectively. We applied corrections to the measured positions for the varying thermal deformation of the antennas on the different days of the VLBI and survey measurements, which can amount to 1 mm, bringing all results to a common reference temperature. The difference between the VLBI and survey results are 0.2 ± 0.4 mm, −1.3 ± 0.4 mm, and 0.8 ± 0.8 mm in the East, North, and Up topocentric components, respectively. We also estimate that the Up component of the baseline may suffer from systematic errors due to gravitational deformation and uncalibrated instrumental delay variations at the 20 m antenna that may reach ± 10 and −2 mm, respectively, resulting in an accuracy uncertainty on the order of 10 mm for the relative heights of the antennas. Furthermore, possible tilting of the 12 m antenna increases the uncertainties in the differences in the horizontal components to 1.0 mm. These results bring into focus the importance of (1) correcting to a common reference temperature the measurements of the reference points of all geodetic instruments within a site, (2) obtaining measurements of the gravitational deformation of all antennas, and (3) monitoring local motions of the geodetic instruments. These results have significant implications for the accuracy of global reference frames that require a
- Published
- 2021
47. An assessment of the accuracy of the VGOS geodetic products
- Author
-
Mondal, Dhiman, Elosegui, Pedro, Barrett, John, Corey, Brian E., Niell, Arthur E., Ruszczyk, Chester A., Titus, Michael A., Behrend, Dirk, Bolotin, Sergei, Gipson, John M., and Macmillan, Daniel S.
- Abstract
American Geophysical Union (AGU) Fall Meeting, 13-17 December 2021, New Orleans, The next-generation VLBI system called VGOS (VLBI Global Observing System) is now operational. A network of 8 VGOS stations has been observing bi-weekly since 2019 under the auspices of the International VLBI Service for Geodesy and Astrometry (IVS) for the creation of standard geodetic products. Moreover, a subset of 2-4 of those VGOS stations has also been observing, starting in 2020, in a VLBI Intensives-like mode to assess the feasibility of earth¿s rotation (UT1) estimation using VGOS. Intensives are VLBI observations that are run on a daily basis using a single baseline, for instance, between Kokee Park Geophysical Observatory, Hawaii, and Wettzell Observatory, Germany, with the goal of near-real time monitoring of UT1. We will describe the VGOS observations, correlation, post-processing, and preliminary geodetic results, including UT1. We will compare the VGOS estimates to estimates from legacy VLBI and other geodetic techniques such as GNSS, when and where possible, to draw some conclusions on the precision and accuracy of the VGOS estimates
- Published
- 2020
48. Effects on geodetic VLBI measurements due to polarization leakage in S/X receivers
- Author
-
Bertarini, Alessandra, Roy, Alan L., Corey, Brian, Walker, R. Craig, Alef, Walter, and Nothnagel, Axel
- Published
- 2011
- Full Text
- View/download PDF
49. A preliminary assessment of the accuracy of the VGOS geodetic products: implications for the terrestrial reference frame and Earth orientation parameters
- Author
-
Mondal, Dhiman, primary, Elosegui, Pedro, additional, Barrett, John, additional, Corey, Brian, additional, Niell, Arthur, additional, Ruszczyk, Chester, additional, and Titus, Michael, additional
- Published
- 2021
- Full Text
- View/download PDF
50. Methodological Reinforcements: Investigating Work Through Trace Data and Text
- Author
-
Laura C. Anderson, Corey Brian Jackson, and Cheryl A. Kieliszewski
- Subjects
Computer tools ,Work (electrical) ,Computer science ,Process (engineering) ,Scientific discovery ,Context (language use) ,Data science ,TRACE (psycholinguistics) - Abstract
In this article, we present a study of scientific discovery through trace data. Using data produced from (1) scientists’ interactions on computer systems and (2) meeting transcripts generated from weekly project meetings, we analyzed the interactions and conversations of scientists surrounding a scientific discovery to determine whether trace data could provide markers for the discovery. The results describe the process of interacting with computer tools and disseminating results and highlight such markers. This study shows trace data, and advanced computational techniques are useful mechanisms for identifying work trajectories and, in some cases, provide context to work behaviors.
- Published
- 2020
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