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6 results on '"Eksteen, N"'

1. Mitigating calibration errors from mutual coupling with time-domain filtering of 21 cm cosmological radio observations

Author

Charles, N., Kern, N. S., Pascua, R., Bernardi, G., Bester, L., Smirnov, O., Acedo, E. d. L., Abdurashidova, Z., Adams, T., Aguirre, J. E., Baartman, R., Beardsley, A. P., Berkhout, L. M., Billings, T. S., Bowman, J. D., Bull, P., Burba, J., Byrne, R., Carey, S., Chen, K., Choudhuri, S., Cox, T., DeBoer, D. R., Dexter, M., Dillon, J. S., Dynes, S., Eksteen, N., Ely, J., Ewall-Wice, A., Fritz, R., Furlanetto, S. R., Gale-Sides, K., Garsden, H., Gehlot, B. K., Ghosh, A., Gorce, A., Gorthi, D., Halday, Z., Hazelton, B. J., Hewitt, J. N., Hickish, J., Huang, T., Jacobs, D. C., Josaitis, A., Kerrigan, J., Kittiwisit, P., Kolopanis, M., Lanman, A., Liu, A., Ma, Y. -Z., MacMahon, D. H. E., Malan, L., Malgas, K., Malgas, C., Marero, B., Martinot, Z. E., McBride, L., Mesinger, A., Mohamed-Hinds, N., Molewa, M., Morales, M. F., Murray, S., Nikolic, B., Nuwegeld, H., Parsons, A. R., Patra, N., Plante, P. L., Qin, Y., Rath, E., Razavi-Ghods, N., Riley, D., Robnett, J., Rosie, K., Santos, M. G., Sims, P., Singh, S., Storer, D., Swarts, H., Tan, J., Wilensky, M. J., Williams, P. K. G., Wyngaarden, P. v., and Zheng, H.

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionisation (EoR). This has led to the construction of low-frequency radio interferometric arrays, such as the Hydrogen Epoch of Reionization Array (HERA), aimed at systematically mapping this emission for the first time. Precision calibration, however, is a requirement in 21 cm radio observations. Due to the spatial compactness of HERA, the array is prone to the effects of mutual coupling, which inevitably lead to non-smooth calibration errors that contaminate the data. When unsmooth gains are used in calibration, intrinsically spectrally-smooth foreground emission begins to contaminate the data in a way that can prohibit a clean detection of the cosmological EoR signal. In this paper, we show that the effects of mutual coupling on calibration quality can be reduced by applying custom time-domain filters to the data prior to calibration. We find that more robust calibration solutions are derived when filtering in this way, which reduces the observed foreground power leakage. Specifically, we find a reduction of foreground power leakage by 2 orders of magnitude at k=0.5.

Published
2024

2. Investigating Mutual Coupling in the Hydrogen Epoch of Reionization Array and Mitigating its Effects on the 21-cm Power Spectrum

Author

Rath, E., Pascua, R., Josaitis, A. T., Ewall-Wice, A., Fagnoni, N., Acedo, E. de Lera, Martinot, Z. E., Abdurashidova, Z., Adams, T., Aguirre, J. E., Baartman, R., Beardsley, A. P., Berkhout, L. M., Bernardi, G., Billings, T. S., Bowman, J. D., Bull, P., Burba, J., Byrne, R., Carey, S., Chen, K. -F., Choudhuri, S., Cox, T., DeBoer, D. R., Dexter, M., Dillon, J. S., Dynes, S., Eksteen, N., Ely, J., Fritz, R., Furlanetto, S. R., Gale-Sides, K., Garsden, H., Gehlot, B. K., Ghosh, A., Gorce, A., Gorthi, D., Halday, Z., Hazelton, B. J., Hewitt, J. N., Hickish, J., Huang, T., Jacobs, D. C., Kern, N. S., Kerrigan, J., Kittiwisit, P., Kolopanis, M., Lanman, A., Liu, A., Ma, Y. -Z., MacMahon, D. H. E., Malan, L., Malgas, C., Malgas, K., Marero, B., McBride, L., Mesinger, A., Mohamed-Hinds, N., Molewa, M., Morales, M. F., Murray, S. G., Nikolic, B., Nuwegeld, H., Parsons, A. R., Patra, N., La Plante, P., Qin, Y., Razavi-Ghods, N., Riley, D., Robnett, J., Rosie, K., Santos, M. G., Sims, P., Singh, S., Storer, D., Swarts, H., Tan, J., Wilensky, M. J., Williams, P. K. G., van Wyngaarden, P., and Zheng, H.

Subjects
Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Interferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on the 21-cm power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be overcome in order to detect the 21-cm signal, and simulations that reproduce effects seen in the data can guide strategies for mitigating mutual coupling. In this paper, we analyse 12 nights of data from the Hydrogen Epoch of Reionization Array and compare the data against simulations that include a computationally efficient and physically motivated semi-analytic treatment of mutual coupling. We find that simulated coupling features qualitatively agree with coupling features in the data; however, coupling features in the data are brighter than the simulated features, indicating the presence of additional coupling mechanisms not captured by our model. We explore the use of fringe-rate filters as mutual coupling mitigation tools and use our simulations to investigate the effects of mutual coupling on a simulated cosmological 21-cm power spectrum in a "worst case" scenario where the foregrounds are particularly bright. We find that mutual coupling contaminates a large portion of the "EoR Window", and the contamination is several orders-of-magnitude larger than our simulated cosmic signal across a wide range of cosmological Fourier modes. While our fiducial fringe-rate filtering strategy reduces mutual coupling by roughly a factor of 100 in power, a non-negligible amount of coupling cannot be excised with fringe-rate filters, so more sophisticated mitigation strategies are required., Comment: 19 pages, 12 figures, submitted to MNRAS

Published
2024

3. Characterization of inpaint residuals in interferometric measurements of the epoch of reionization

Author

Pagano, M, Liu, J, Liu, A, Kern, NS, Ewall-Wice, A, Bull, P, Pascua, R, Ravanbakhsh, S, Abdurashidova, Z, Adams, T, Aguirre, JE, Alexander, P, Ali, ZS, Baartman, R, Balfour, Y, Beardsley, AP, Bernardi, G, Billings, TS, Bowman, JD, Bradley, RF, Burba, J, Carey, S, Carilli, CL, Cheng, C, DeBoer, DR, Acedo, EDL, Dexter, M, Dillon, JS, Eksteen, N, Ely, J, Fagnoni, N, Fritz, R, Furlanetto, SR, Gale-Sides, K, Glendenning, B, Gorthi, D, Greig, B, Grobbelaar, J, Halday, Z, Hazelton, BJ, Hewitt, JN, Hickish, J, Jacobs, DC, Julius, A, Kariseb, M, Kerrigan, J, Kittiwisit, P, Kohn, SA, Kolopanis, M, Lanman, A, La Plante, P, Loots, A, MacMahon, DHE, Malan, L, Malgas, C, Malgas, K, Marero, B, Martinot, ZE, Mesinger, A, Molewa, M, Morales, MF, Mosiane, T, Neben, AR, Nikolic, B, Nuwegeld, H, Parsons, AR, Patra, N, Pieterse, S, Razavi-Ghods, N, Robnett, J, Rosie, K, Sims, P, Smith, C, Swarts, H, Thyagarajan, N, van Wyngaarden, P, Williams, PKG, Zheng, H, Pagano, M, Liu, J, Liu, A, Kern, NS, Ewall-Wice, A, Bull, P, Pascua, R, Ravanbakhsh, S, Abdurashidova, Z, Adams, T, Aguirre, JE, Alexander, P, Ali, ZS, Baartman, R, Balfour, Y, Beardsley, AP, Bernardi, G, Billings, TS, Bowman, JD, Bradley, RF, Burba, J, Carey, S, Carilli, CL, Cheng, C, DeBoer, DR, Acedo, EDL, Dexter, M, Dillon, JS, Eksteen, N, Ely, J, Fagnoni, N, Fritz, R, Furlanetto, SR, Gale-Sides, K, Glendenning, B, Gorthi, D, Greig, B, Grobbelaar, J, Halday, Z, Hazelton, BJ, Hewitt, JN, Hickish, J, Jacobs, DC, Julius, A, Kariseb, M, Kerrigan, J, Kittiwisit, P, Kohn, SA, Kolopanis, M, Lanman, A, La Plante, P, Loots, A, MacMahon, DHE, Malan, L, Malgas, C, Malgas, K, Marero, B, Martinot, ZE, Mesinger, A, Molewa, M, Morales, MF, Mosiane, T, Neben, AR, Nikolic, B, Nuwegeld, H, Parsons, AR, Patra, N, Pieterse, S, Razavi-Ghods, N, Robnett, J, Rosie, K, Sims, P, Smith, C, Swarts, H, Thyagarajan, N, van Wyngaarden, P, Williams, PKG, and Zheng, H

Abstract

To mitigate the effects of Radio Frequency Interference (RFI) on the data analysis pipelines of 21 cm interferometric instruments, numerous inpaint techniques have been developed. In this paper, we examine the qualitative and quantitative errors introduced into the visibilities and power spectrum due to inpainting. We perform our analysis on simulated data as well as real data from the Hydrogen Epoch of Reionization Array (HERA) Phase 1 upper limits. We also introduce a convolutional neural network that is capable of inpainting RFI corrupted data. We train our network on simulated data and show that our network is capable of inpainting real data without requiring to be retrained. We find that techniques that incorporate high wavenumbers in delay space in their modelling are best suited for inpainting over narrowband RFI. We show that with our fiducial parameters discrete prolate spheroidal sequences (dpss) and clean provide the best performance for intermittent RFI while Gaussian progress regression (gpr) and least squares spectral analysis (lssa) provide the best performance for larger RFI gaps. However, we caution that these qualitative conclusions are sensitive to the chosen hyperparameters of each inpainting technique. We show that all inpainting techniques reliably reproduce foreground dominated modes in the power spectrum. Since the inpainting techniques should not be capable of reproducing noise realizations, we find that the largest errors occur in the noise dominated delay modes. We show that as the noise level of the data comes down, clean and dpss are most capable of reproducing the fine frequency structure in the visibilities.

Published
2023

4. Bayesian jackknife tests with a small number of subsets: application to HERA 21 cm power spectrum upper limits

Author

Wilensky, MJ, Kennedy, F, Bull, P, Dillon, JS, Abdurashidova, Z, Adams, T, Aguirre, JE, Alexander, P, Ali, ZS, Baartman, R, Balfour, Y, Beardsley, AP, Bernardi, G, Billings, TS, Bowman, JD, Bradley, RF, Burba, J, Carey, S, Carilli, CL, Cheng, C, DeBoer, DR, de Lera Acedo, E, Dexter, M, Eksteen, N, Ely, J, Ewall-Wice, A, Fagnoni, N, Fritz, R, Furlanetto, SR, Gale-Sides, K, Glendenning, B, Gorthi, D, Greig, B, Grobbelaar, J, Halday, Z, Hazelton, BJ, Hewitt, JN, Hickish, J, Jacobs, DC, Julius, A, Kariseb, M, Kern, NS, Kerrigan, J, Kittiwisit, P, Kohn, SA, Kolopanis, M, Lanman, A, La Plante, P, Liu, A, Loots, A, MacMahon, DHE, Malan, L, Malgas, C, Malgas, K, Marero, B, Martinot, ZE, Mesinger, A, Molewa, M, Morales, MF, Mosiane, T, Murray, SG, Neben, AR, Nikolic, B, Nuwegeld, H, Parsons, AR, Patra, N, Pieterse, S, Razavi-Ghods, N, Robnett, J, Rosie, K, Sims, P, Swarts, H, Thyagarajan, N, van Wyngaarden, P, Williams, PKG, Zheng, H, Wilensky, MJ, Kennedy, F, Bull, P, Dillon, JS, Abdurashidova, Z, Adams, T, Aguirre, JE, Alexander, P, Ali, ZS, Baartman, R, Balfour, Y, Beardsley, AP, Bernardi, G, Billings, TS, Bowman, JD, Bradley, RF, Burba, J, Carey, S, Carilli, CL, Cheng, C, DeBoer, DR, de Lera Acedo, E, Dexter, M, Eksteen, N, Ely, J, Ewall-Wice, A, Fagnoni, N, Fritz, R, Furlanetto, SR, Gale-Sides, K, Glendenning, B, Gorthi, D, Greig, B, Grobbelaar, J, Halday, Z, Hazelton, BJ, Hewitt, JN, Hickish, J, Jacobs, DC, Julius, A, Kariseb, M, Kern, NS, Kerrigan, J, Kittiwisit, P, Kohn, SA, Kolopanis, M, Lanman, A, La Plante, P, Liu, A, Loots, A, MacMahon, DHE, Malan, L, Malgas, C, Malgas, K, Marero, B, Martinot, ZE, Mesinger, A, Molewa, M, Morales, MF, Mosiane, T, Murray, SG, Neben, AR, Nikolic, B, Nuwegeld, H, Parsons, AR, Patra, N, Pieterse, S, Razavi-Ghods, N, Robnett, J, Rosie, K, Sims, P, Swarts, H, Thyagarajan, N, van Wyngaarden, P, Williams, PKG, and Zheng, H

Abstract

We present a Bayesian jackknife test for assessing the probability that a data set contains biased subsets, and, if so, which of the subsets are likely to be biased. The test can be used to assess the presence and likely source of statistical tension between different measurements of the same quantities in an automated manner. Under certain broadly applicable assumptions, the test is analytically tractable. We also provide an open-source code, chiborg, that performs both analytic and numerical computations of the test on general Gaussian-distributed data. After exploring the information theoretical aspects of the test and its performance with an array of simulations, we apply it to data from the Hydrogen Epoch of Reionization Array (HERA) to assess whether different sub-seasons of observing can justifiably be combined to produce a deeper 21 cm power spectrum upper limit. We find that, with a handful of exceptions, the HERA data in question are statistically consistent and this decision is justified. We conclude by pointing out the wide applicability of this test, including to CMB experiments and the H0 tension.

Published
2023

5. Direct Optimal Mapping for 21cm Cosmology: A Demonstration with the Hydrogen Epoch of Reionization Array

Author

Xu, Z, Hewitt, JN, Chen, KF, Kim, H, Dillon, JS, Kern, NS, Morales, MF, Hazelton, BJ, Byrne, R, Fagnoni, N, Acedo, EDL, Abdurashidova, Z, Adams, T, Aguirre, JE, Alexander, P, Ali, ZS, Baartman, R, Balfour, Y, Beardsley, AP, Bernardi, G, Billings, TS, Bowman, JD, Bradley, RF, Bull, P, Burba, J, Carey, S, Carilli, CL, Cheng, C, DeBoer, DR, Dexter, M, Eksteen, N, Ely, J, Ewall-Wice, A, Fritz, R, Furlanetto, Gale-Sides, K, Glendenning, B, Gorthi, D, Greig, B, Grobbelaar, J, Halday, Z, Hickish, J, Jacobs, DC, Julius, A, Kariseb, M, Kerrigan, J, Kittiwisit, P, Kohn, SA, Kolopanis, M, Lanman, A, Plante, PL, Liu, A, Loots, A, Ma, YZ, Edward MacMahon, DH, Malan, L, Malgas, C, Malgas, K, Marero, B, Martinot, ZE, Mesinger, A, Molewa, M, Mosiane, T, Murray, SG, Neben, AR, Nikolic, B, Nuwegeld, H, Parsons, AR, Patra, N, Pieterse, S, Pober, JC, Razavi-Ghods, N, Robnett, J, Rosie, K, Sims, P, Smith, C, Swarts, H, Thyagarajan, N, Wyngaarden, PVV, Williams, PKG, Zheng, H, Xu, Z [0000-0001-5112-2567], Hewitt, JN [0000-0002-4117-570X], Chen, KF [0000-0002-3839-0230], Dillon, JS [0000-0003-3336-9958], Kern, NS [0000-0002-8211-1892], Morales, MF [0000-0001-7694-4030], Hazelton, BJ [0000-0001-7532-645X], Byrne, R [0000-0003-4980-2736], Aguirre, JE [0000-0002-4810-666X], Beardsley, AP [0000-0001-9428-8233], Bernardi, G [0000-0002-0916-7443], Bowman, JD [0000-0002-8475-2036], Bradley, RF [0000-0003-1172-8331], Bull, P [0000-0001-5668-3101], Carilli, CL [0000-0001-6647-3861], DeBoer, DR [0000-0003-3197-2294], Ewall-Wice, A [0000-0002-0086-7363], Furlanetto, SR [0000-0002-0658-1243], Gorthi, D [0000-0002-0829-167X], Greig, B [0000-0002-4085-2094], Jacobs, DC [0000-0002-0917-2269], Kerrigan, J [0000-0002-1876-272X], Kittiwisit, P [0000-0003-0953-313X], Kohn, SA [0000-0001-6744-5328], Kolopanis, M [0000-0002-2950-2974], Lanman, A [0000-0003-2116-3573], Plante, PL [0000-0002-4693-0102], Liu, A [0000-0001-6876-0928], Ma, YZ [0000-0001-8108-0986], Mesinger, A [0000-0003-3374-1772], Murray, SG [0000-0003-3059-3823], Neben, AR [0000-0001-7776-7240], Parsons, AR [0000-0002-5400-8097], Patra, N [0000-0002-9457-1941], Pober, JC [0000-0002-3492-0433], Sims, P [0000-0002-2871-0413], Thyagarajan, N [0000-0003-1602-7868], Williams, PKG [0000-0003-3734-3587], Apollo - University of Cambridge Repository, Xu, Zhilei, Hewitt, Jacqueline N., Chen, Kai-Feng, Kim, Honggeun, Dillon, Joshua S., Kern, Nicholas S., Morales, Miguel F., Hazelton, Bryna J., Byrne, Ruby, Fagnoni, Nicola, de Lera Acedo, Eloy, Abdurashidova, Zara, Adams, Tyrone, Aguirre, James E., Alexander, Paul, Ali, Zaki S., Baartman, Rushelle, Balfour, Yanga, Beardsley, Adam P., Bernardi, Gianni, Billings, Tashalee S., Bowman, Judd D., Bradley, Richard F., Bull, Philip, Burba, Jacob, Carey, Steven, Carilli, Chris L., Cheng, Carina, Deboer, David R., Dexter, Matt, Eksteen, Nico, Ely, John, Ewall-Wice, Aaron, Fritz, Randall, Furlanetto, Steven R., Gale-Sides, Kingsley, Glendenning, Brian, Gorthi, Deepthi, Greig, Bradley, Grobbelaar, Jasper, Halday, Ziyaad, Hickish, Jack, Jacobs, Daniel C., Julius, Austin, Kariseb, Maccalvin, Kerrigan, Joshua, Kittiwisit, Piyanat, Kohn, Saul A., Kolopanis, Matthew, Lanman, Adam, La Plante, Paul, Liu, Adrian, Loots, Anita, Ma, Yin-Zhe, Harold Edward MacMahon, David, Malan, Lourence, Malgas, Cresshim, Malgas, Keith, Marero, Bradley, Martinot, Zachary E., Mesinger, ANDREI ALBERT, Molewa, Mathakane, Mosiane, Tshegofalang, Murray, Steven G., Neben, Abraham R., Nikolic, Bojan, Nuwegeld, Han, Parsons, Aaron R., Patra, Nipanjana, Pieterse, Samantha, Pober, Jonathan C., Razavi-Ghods, Nima, Robnett, Jame, Rosie, Kathryn, Sims, Peter, Smith, Craig, Swarts, Hilton, Thyagarajan, Nithyanandan, Van Van Wyngaarden, Pieter, Williams, Peter K. G., and Zheng, Haoxuan

Subjects
Cosmology and Nongalactic Astrophysics (astro-ph.CO), model, maps, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Galactic radio-emission, 5109 Space Sciences, power spectrum, calibration, 10 mhz, Settore FIS/05 - Astronomia e Astrofisica, 5101 Astronomical Sciences, Space and Planetary Science, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), upper limit, 51 Physical Sciences, 5107 Particle and High Energy Physics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

Motivated by the desire for wide-field images with well-defined statistical properties for 21cm cosmology, we implement an optimal mapping pipeline that computes a maximum likelihood estimator for the sky using the interferometric measurement equation. We demonstrate this direct optimal mapping with data from the Hydrogen Epoch of Reionization (HERA) Phase I observations. After validating the pipeline with simulated data, we develop a maximum likelihood figure-of-merit for comparing four sky models at 166MHz with a bandwidth of 100kHz. The HERA data agree with the GLEAM catalogs to, 16 pages, 10 figures, 2 tables, published on ApJ

Published
2022

6. Isolation and significance of anaerobic bacteria isolated from cases of bovine mastitis.

Author

Du Preez JH, Greeff AS, and Eksteen N

Subjects
Animals, Bacteroides fragilis isolation & purification, Cattle, Eubacterium isolation & purification, Mammary Glands, Animal microbiology, Peptococcus isolation & purification, Propionibacterium isolation & purification, Streptococcus isolation & purification, Mastitis, Bovine microbiology
Abstract

The role of obligate anaerobic bacteria in the aetiology of mastitis of lactating dairy cows was investigated. Anaerobes were isolated from 12% of lactating mastitic cows, which were representative of 50% of the 10 dairy herds examined. Bacteroides fragilis was the most frequently isolated organism of (50%), followed by Peptococcus indolicus (33%), Eubacterium lentum (33%), E. aerofaciens (17%), Propionibacterium granulosum (17%) and an anaerobic Streptococcus sp. (17%). These obligate anaerobes were always isolated together with organisms classically involved in mastitis. It was possible to induce overt clinical mastitis in healthy lactating udders within 24 hours by infection with single pure cultures of anaerobes via the teat canal. All B. fragilis strains were resistant to penicillin G and tetracycline. In addition, one strain was also resistant to ampicillin, cephalothin and amoxicillin. Anaerobic gram positive cocci and bacilli were sensitive to most antibiotics. These findings imply an important role for anaerobes in the aetiology of mastitis.

Published
1981

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