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19 results on '"Honggeun Kim"'

1. Direct Optimal Mapping Image Power Spectrum and its Window Functions

Author

Zhilei Xu, Honggeun Kim, Jacqueline N. Hewitt, Kai-Feng Chen, Nicholas S. Kern, Eleanor Rath, Ruby Byrne, Adélie Gorce, Robert Pascua, Zachary E. Martinot, Joshua S. Dillon, Bryna J. Hazelton, Adrian Liu, Miguel F. Morales, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Chris L. Carilli, Carina Cheng, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Nico Eksteen, John Ely, Aaron Ewall-Wice, Nicolas Fagnoni, Randall Fritz, Steven R. Furlanetto, Kingsley Gale-Sides, Brian Glendenning, Deepthi Gorthi, Bradley Greig, Jasper Grobbelaar, Ziyaad Halday, Jack Hickish, Daniel C. Jacobs, Austin Julius, MacCalvin Kariseb, Joshua Kerrigan, Piyanat Kittiwisit, Saul A. Kohn, Matthew Kolopanis, Adam Lanman, Paul La Plante, Anita Loots, David Harold Edward MacMahon, Lourence Malan, Cresshim Malgas, Keith Malgas, Bradley Marero, Andrei Mesinger, Mathakane Molewa, Tshegofalang Mosiane, Steven G. Murray, Abraham R. Neben, Bojan Nikolic, Hans Nuwegeld, Aaron R. Parsons, Nipanjana Patra, Samantha Pieterse, Nima Razavi-Ghods, James Robnett, Kathryn Rosie, Peter Sims, Craig Smith, Hilton Swarts, Jianrong Tan, Nithyanandan Thyagarajan, Pieter van Wyngaarden, Peter K. G. Williams, Haoxuan Zheng, and HERA Collaboration

Subjects
H I line emission, Radio interferometry, Early universe, Reionization, Astrophysics, QB460-466
Abstract

The key to detecting neutral hydrogen during the epoch of reionization (EoR) is to separate the cosmological signal from the dominating foreground radiation. We developed direct optimal mapping (DOM) to map interferometric visibilities; it contains only linear operations, with full knowledge of point spread functions from visibilities to images. Here, we demonstrate a fast Fourier transform-based image power spectrum and its window functions computed from the DOM images. We use noiseless simulation, based on the Hydrogen Epoch of Reionization Array Phase I configuration, to study the image power spectrum properties. The window functions show

Published
2024
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2. The Impact of Beam Variations on Power Spectrum Estimation for 21 cm Cosmology. II. Mitigation of Foreground Systematics for HERA

Author

Honggeun Kim, Nicholas S. Kern, Jacqueline N. Hewitt, Bang D. Nhan, Joshua S. Dillon, Eloy de Lera Acedo, Scott B. C. Dynes, Nivedita Mahesh, Nicolas Fagnoni, and David R. DeBoer

Subjects
Cosmology, Reionization, Radio astronomy, Radio interferometers, Astronomical instrumentation, Astrophysics, QB460-466
Abstract

One key challenge in detecting a 21 cm cosmological signal at z > 6 is to separate the cosmological signal from foreground emission. This can be studied in a power spectrum space where the foreground is confined to low delay (or, equivalently, k _∥ ) modes, whereas the cosmological signal can spread out to high delay modes. When there is a calibration error, however, the chromaticity of the gain errors propagates to the power spectrum estimate and contaminates the modes for cosmological detection. The Hydrogen Epoch of Reionization Array (HERA) employs a high-precision calibration scheme using redundancy in measurements. In this study, we focus on the gain errors induced by nonredundancies arising from a feed offset relative to HERA’s 14 m parabolic dish element and investigate how to mitigate the chromatic gain errors using three different methods: restricting baseline lengths for calibration, smoothing the antenna gains, and applying a temporal filter prior to calibration. With 2 cm/2° perturbations for translation/tilting motions, a level achievable under normal HERA operating conditions, the combination of the baseline cut and temporal filtering indicates that the spurious gain feature due to nonredundancies is significantly reduced, and the power spectrum recovers the clean foreground-free region. We found that the mitigation technique works even for large feed motions, but in order to keep a stable calibration process, the feed positions need to be constrained to 2 cm for translation motions and 2° for tilting offset relative to the dish’s vertex.

Published
2023
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16. Imaging and Modeling Data from the Hydrogen Epoch of Reionization Array

Author

Juan Mena Parra, Piyanat Kittiwisit, Kingsley Gale-Sides, Joshua Kerrigan, Honggeun Kim, Adrian Liu, Phil Bull, Nipanjana Patra, Ziyaad Halday, Matthys Maree, James E. Aguirre, Bryna J. Hazelton, Jacqueline N. Hewitt, Zara Abdurashidova, Saul A. Kohn, Judd D. Bowman, Matt Dexter, K. Gale-Sides, Samantha Pieterse, Paul La Plante, Mathakane Molewa, James Kent, Nithyanandan Thyagarajan, Eunice Matsetela, Nicolas Fagnoni, Adam P. Beardsley, Alec Josaitis, Kathryn Rosie, David MacMahon, Jonathan C. Pober, Andrei Mesinger, Jasper Grobbelaar, Tashalee S. Billings, Zachary E. Martinot, Tshegofalang Mosiane, Abraham R. Neben, Austin Julius, Randall Fritz, Siyanda Matika, Brian Glendenning, Carina Cheng, Peter Sims, Paul Alexander, Daniel C. Jacobs, Steve R. Furlanetto, Gianni Bernardi, Bradley Greig, Lourence Malan, Nima Razavi-Ghods, Cresshim Malgas, Yanga Balfour, Nicholas S. Kern, Telalo Lekalake, David DeBoer, Aaron R. Parsons, Richard F. Bradley, Matthew Kolopanis, Deepthi Gorthi, Peter K. G. Williams, James Robnett, Joshua S. Dillon, Chris Carilli, Eloy de Lera Acedo, Miguel F. Morales, Zaki S. Ali, Bojan Nikolic, Aaron Ewall-Wice, Jack Hickish, Jacob Burba, Angelo Syce, Haoxuan Zheng, Adam Lanman, ITA, USA, ZAF, Carilli, C. L., Thyagarajan, N., Kent, J., Nikolic, B., Gale-Sides, K., Kern, N. S., Bernardi, G., Mesinger, A., Matika, S., Abdurashidova, Zara, Aguirre, James E., Paul, Alexander Christian, Ali, Zaki S., Balfour, Yanga, Beardsley, Adam P., Billings, Tashalee S., Bowman, Judd D., Bradley, Richard F., Bull, Phil, Burba, Jacob, Cheng, Carina, Deboer, David R., Dexter, Matt, Acedo, Eloy de Lera, Dillon, Joshua S., Ewall-Wice, Aaron, Fagnoni, Nicola, Fritz, Randall, Furlanetto, Steve R., Gale-Sides, Kingsley, Glendenning, Brian, Gorthi, Deepthi, Greig, Bradley, Grobbelaar, Jasper, Halday, Ziyaad, Hazelton, Bryna J., Hewitt, Jacqueline N., Hickish, Jack, Jacobs, Daniel C., Josaitis, Alec, Julius, Austin, Kerrigan, Joshua, Kim, Honggeun, Kittiwisit, Piyanat, Kohn, Saul A., Kolopanis, Matthew, Lanman, Adam, Plante, Paul La, Lekalake, Telalo, Liu, Adrian, Macmahon, David, Malan, Lourence, Malgas, Cresshim, Maree, Matthy, Martinot, Zachary E., Matsetela, Eunice, Molewa, Mathakane, Morales, Miguel F., Mosiane, Tshegofalang, Neben, Abraham R., Parra, Juan Mena, Parsons, Aaron R., Patra, Nipanjana, Pieterse, Samantha, Pober, Jonathan C., Razavi-Ghods, Nima, Robnett, Jame, Rosie, Kathryn, Sims, Peter, Syce, Angelo, Williams, Peter K. G., Zheng, Haoxuan, Carilli, CL [0000-0001-6647-3861], Thyagarajan, N [0000-0003-1602-7868], Kern, NS [0000-0002-8211-1892], Bernardi, G [0000-0002-0916-7443], Aguirre, JE [0000-0002-4810-666X], Beardsley, AP [0000-0001-9428-8233], Bowman, JD [0000-0002-8475-2036], Bull, P [0000-0001-5668-3101], Dillon, JS [0000-0003-3336-9958], Ewall-Wice, A [0000-0002-0086-7363], Furlanetto, SR [0000-0002-0658-1243], Hazelton, BJ [0000-0001-7532-645X], 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], Liu, A [0000-0001-6876-0928], Morales, MF [0000-0001-7694-4030], Neben, AR [0000-0001-7776-7240], Patra, N [0000-0002-9457-1941], Pober, JC [0000-0002-3492-0433], Williams, PKG [0000-0003-3734-3587], and Apollo - University of Cambridge Repository

Subjects
Physics, Cosmological evolution, Hydrogen, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, chemistry.chemical_element, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Cosmology, Data modeling, chemistry, Reionization, Space and Planetary Science, 0103 physical sciences, Radio interferometry, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM)
Abstract

We analyze data from the Hydrogen Epoch of Reionization Array. This is the third in a series of papers on the closure phase delay-spectrum technique designed to detect the HI 21cm emission from cosmic reionization. We present the details of the data and models employed in the power spectral analysis, and discuss limitations to the process. We compare images and visibility spectra made with HERA data, to parallel quantities generated from sky models based on the GLEAM survey, incorporating the HERA telescope model. We find reasonable agreement between images made from HERA data, with those generated from the models, down to the confusion level. For the visibility spectra, there is broad agreement between model and data across the full band of $\sim 80$MHz. However, models with only GLEAM sources do not reproduce a roughly sinusoidal spectral structure at the tens of percent level seen in the observed visibility spectra on scales $\sim 10$ MHz on 29 m baselines. We find that this structure is likely due to diffuse Galactic emission, predominantly the Galactic plane, filling the far sidelobes of the antenna primary beam. We show that our current knowledge of the frequency dependence of the diffuse sky radio emission, and the primary beam at large zenith angles, is inadequate to provide an accurate reproduction of the diffuse structure in the models. We discuss implications due to this missing structure in the models, including calibration, and in the search for the HI 21cm signal, as well as possible mitigation techniques., Comment: 17 pages, 10 figures, accepted for the ApJ Supplement

Published
2020

17. Understanding the HERA Phase I receiver system with simulations and its impact on the detectability of the EoR delay power spectrum

Author

Richard F. Bradley, Matthew Kolopanis, Nithyanandan Thyagarajan, Adam Lanman, Lourence Malan, Saul A. Kohn, Alec Josaitis, Adrian Liu, Bryna J. Hazelton, Matt Dexter, Haoxuan Zheng, Piyanat Kittiwisit, Nicholas S. Kern, Kingsley Gale-Sides, Deepthi Gorthi, Joshua S. Dillon, Paul Alexander, Honggeun Kim, Craig Smith, Miguel F. Morales, Steve R. Furlanetto, Adam P. Beardsley, Mathakane Molewa, Zaki S. Ali, Bojan Nikolic, Aaron Ewall-Wice, Tshegofalang Mosiane, Phil Bull, Nipanjana Patra, Jacqueline N. Hewitt, Ziyaad Halday, Angelo Syce, Abraham R. Neben, Randall Fritz, Juan Mena Parra, Jack Hickish, Aaron R. Parsons, Joshua Kerrigan, Brian Glendenning, Carina Cheng, Paul La Plante, James Robnett, Jacob Burba, Chris Carilli, Eloy de Lera Acedo, Telalo Lekalake, Zara Abdurashidova, Kathryn Rosie, Gianni Bernardi, David MacMahon, Austin Julius, Daniel C. Jacobs, Nima Razavi-Ghods, Cresshim Malgas, Nicolas Fagnoni, Yanga Balfour, Matthys Maree, Peter Sims, Jonathan C. Pober, Andrei Mesinger, Jasper Grobbelaar, Tashalee S. Billings, Zachary E. Martinot, Bradley Greig, James E. Aguirre, Peter K. G. Williams, Eunice Matsetela, Judd D. Bowman, Samantha Pieterse, David DeBoer, ITA, USA, GBR, Fagnoni, N., De Lera Acedo, E., Deboer, D. R., Abdurashidova, Z., Aguirre, J. E., Alexander, P., Ali, Z. S., Balfour, Y., Beardsley, A. P., Bernardi, G., Billings, T. S., Bowman, J. D., Bradley, R. F., Bull, P., Burba, J., Carilli, C. L., Cheng, C., Dexter, M., Dillon, J. S., Ewall-Wice, A., Fritz, R., Furlanetto, S. R., Gale-Sides, K., Glendenning, B., Gorthi, D., Greig, B., Grobbelaar, J., Halday, Z., Hazelton, B. J., Hewitt, J. N., Hickish, J., Jacobs, D. C., Josaitis, A., Julius, A., Kern, N. S., Kerrigan, J., Kim, H., Kittiwisit, P., Kohn, S. A., Kolopanis, M., Lanman, A., Plante, P. L., Lekalake, T., Liu, A., Macmahon, D., Malan, L., Malgas, C., Maree, M., Martinot, Z. E., Matsetela, E., Mena Parra, J., Mesinger, A., Molewa, M., Morales, M. F., Mosiane, T., Neben, A. R., Nikolic, B., Parsons, A. R., Patra, N., Pieterse, S., Pober, J. C., Razavi-Ghods, N., Robnett, J., Rosie, K., Sims, P., Smith, C., Syce, A., Thyagarajan, N., Williams, P. K. G., and Zheng, H.

Subjects
interferometers [instrumentation], first stars, Phase (waves), FOS: Physical sciences, 02 engineering and technology, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, 01 natural sciences, law.invention, Radio telescope, Telescope, Optics, Settore FIS/05 - Astronomia e Astrofisica, law, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, dark ages, 010303 astronomy & astrophysics, Reionization, Instrumentation and Methods for Astrophysics (astro-ph.IM), Physics, business.industry, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, 020206 networking & telecommunications, Astronomy and Astrophysics, numerical [methods], telescopes, HERA, interferometric [techniques], interferometer [instrumentation], Transmission (telecommunications), Space and Planetary Science, reionization, dark ages, reionization, first star, Antenna (radio), Astrophysics - Instrumentation and Methods for Astrophysics, business, Astronomical and Space Sciences, astro-ph.IM
Abstract

The detection of the Epoch of Reionization (EoR) delay power spectrum using a "foreground avoidance method" highly depends on the instrument chromaticity. The systematic effects induced by the radio-telescope spread the foreground signal in the delay domain, which contaminates the EoR window theoretically observable. Applied to the Hydrogen Epoch of Reionization Array (HERA), this paper combines detailed electromagnetic and electrical simulations in order to model the chromatic effects of the instrument, and quantify its frequency and time responses. In particular, the effects of the analogue receiver, transmission cables, and mutual coupling are included. These simulations are able to accurately predict the intensity of the reflections occurring in the 150-m cable which links the antenna to the back-end. They also show that electromagnetic waves can propagate from one dish to another one through large sections of the array due to mutual coupling. The simulated system time response is attenuated by a factor $10^{4}$ after a characteristic delay which depends on the size of the array and on the antenna position. Ultimately, the system response is attenuated by a factor $10^{5}$ after 1400 ns because of the reflections in the cable, which corresponds to characterizable ${k_\parallel}$-modes above 0.7 $h\;\rm{Mpc}^{-1}$ at 150 MHz. Thus, this new study shows that the detection of the EoR signal with HERA Phase I will be more challenging than expected. On the other hand, it improves our understanding of the telescope, which is essential to mitigate the instrument chromaticity., Comment: 13 pages, 17 figures - Submitted to MNRAS - 2nd revision

Published
2019
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19. SoIDPS: Sensor Objects-Based Intrusion Detection and Prevention System and Its Implementation.

Author

Yue Hao, Jiming Liu, Yu-Ping Wang, Yiu-ming Cheung, Hujun Yin, Licheng Jiao, Jianfeng Ma, Yong-Chang Jiao, SeongJe Cho, Hye-Young Chang, HongGeun Kim, and WoongChul Choi

Abstract

In this paper, we propose an intrusion detection and prevention system using sensor objects that are a kind of trap and are accessible only by the programs that are allowed by the system. Any access to the sensor object by disallowed programs or any transmission of the sensor object to outside of the system is regarded as an intrusion. In such case, the proposed system logs the related information on the process as well as the network connections, and terminates the suspicious process to prevent any possible intrusion. By implementing the proposed method as Loadable Kernel Module (LKM) in the Linux, it is impossible for any process to access the sensor objects without permission. In addition, the security policy will be dynamically applied at run time. Experimental results show that the security policy is enforced with negligible overhead, compared to the performance of the unmodified original system. [ABSTRACT FROM AUTHOR]

Published
2005
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