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10. Efficient Storage of Embedded Element Patterns for Low Frequency Radio Telescopes.

Author

Davidson, David B. and Sutinjo, Adrian T.

Subjects
RADIO telescopes, LEGENDRE'S functions, MATHEMATICAL functions, ANTENNAS (Electronics), SPECIAL functions
Abstract

The use of spherical modes offers an efficient solution for storing embedded element patterns with significant angular structure for large scale arrays, such as the Square Kilometer Array (SKA)‐Low radio telescope. These patterns are required for calibration of the numerous stations comprising the telescope, each containing several hundred elements, and operating over a 7:1 bandwidth. However, implementation is significantly complicated by the many differences in the notation used in the literature for the Legendre special functions. The differing phasor conventions used in electrical engineering and physics further complicate this. This paper synthesizes much of the existing literature on this topic, paying special attention to these issues. Mathematical implementation issues are also addressed. A number of suitable tests using canonical dipole radiators to verify correct implementation are outlined. The paper concludes with tests on an individual SKALA4 antenna and a full‐scale SKA‐Low prototype station comprising 256 of these antennas. The storage saving afforded is some three orders of magnitude; this is very significant for a full SKA‐Low station. Supporting material summarizes differing formulations and conventions encountered in the literature. Plain Language Summary: The Square Kilometer Array Observatory aims to significantly advance our understanding of the Universe and the laws of fundamental physics by providing two telescopes of unprecedented capability, located in South Africa and Western Australia (WA). The "low" frequency telescope (in WA), covering radio frequencies from 50 to 350 MHz, comprises a large number of stations, which are groups of antennas. These antennas interact strongly with each other within the station; this interaction is captured via a set of elemental radiation patterns which describe the sensitivity of each antenna as a function of angle on the sky. These patterns are pre‐calculated and used for calibrating the station, which is essential for optimal performance. Storing these patterns by finely sampling them in angle results in very large data sets. Using a special mathematical function known as an associated Legendre function, which captures angular variation over a sphere very efficiently, it is possible to greatly reduce the size of these sets — typically by a factor of around one thousand. However, there are a number of different conventions in use for these functions which makes this difficult to implement. This paper provides a consistent development of the method, supported by a software implementation in MATLAB. Key Points: Embedded element patterns for large arrays can be efficiently stored using spherical modesReconstructing the fields from the stored modes is challenging due to many differences in the notation used in the literatureThis work provides a consistent development of the method, supported by a software implementation in MATLAB [ABSTRACT FROM AUTHOR]

Published
2024
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32. The Streptococcus phage protein paratox is an intrinsically disordered protein.

Author

Asakereh, Iman, Rutbeek, Nicole R., Singh, Manvir, Davidson, David, Prehna, Gerd, and Khajehpour, Mazdak

Abstract

The bacteriophage protein paratox (Prx) blocks quorum sensing in its streptococcal host by directly binding the signal receptor and transcription factor ComR. This reduces the ability of Streptococcus to uptake environmental DNA and protects phage DNA from damage by recombination. Past work characterizing the Prx:ComR molecular interaction revealed that paratox adopts a well‐ordered globular fold when bound to ComR. However, solution‐state biophysical measurements suggested that Prx may be conformationally dynamic. To address this discrepancy, we investigated the stability and dynamic properties of Prx in solution using circular dichroism, nuclear magnetic resonance, and several fluorescence‐based protein folding assays. Our work shows that under dilute buffer conditions Prx is intrinsically disordered. We also show that the addition of kosmotropic salts or protein stabilizing osmolytes induces Prx folding. However, the solute stabilized fold is different from the conformation Prx adopts when it is bound to ComR. Furthermore, we have characterized Prx folding thermodynamics and folding kinetics through steady‐state fluorescence and stopped flow kinetic measurements. Our results show that Prx is a highly dynamic protein in dilute solution, folding and refolding within the 10 ms timescale. Overall, our results demonstrate that the streptococcal phage protein Prx is an intrinsically disordered protein in a two‐state equilibrium with a solute‐stabilized folded form. Furthermore, the solute‐stabilized fold is likely the predominant form of Prx in a solute‐crowded bacterial cell. Finally, our work suggests that Prx binds and inhibits ComR, and thus quorum sensing in Streptococcus, by a combination of conformational selection and induced‐fit binding mechanisms. [ABSTRACT FROM AUTHOR]

Published
2024
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