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Breakthrough Listen is a 10-yr initiative to search for signatures of technologies created by extraterrestrial civilisations at radio and optical wavelengths. Here, we detail the digital data recording system deployed for Breakthrough Listen observations at the 64-m aperture CSIRO Parkes Telescope in New South Wales, Australia. The recording system currently implements two modes: a dual-polarisation, 1.125-GHz bandwidth mode for single-beam observations, and a 26-input, 308-MHz bandwidth mode for the 21-cm multibeam receiver. The system is also designed to support a 3-GHz single-beam mode for the forthcoming Parkes ultra-wideband feed. In this paper, we present details of the system architecture, provide an overview of hardware and software, and present initial performance results.
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 EoR 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.
We review the importance of Centaurus A in high-energy astrophysics as a nearby object with many of the properties expected of a major source of very high-energy cosmic rays and gamma rays. We examine observational techniques and the results so far obtained in the energy range from 200 GeV to above 100 EeV and attempt to fit those data to expectations of Centaurus Aas an astrophysical source from very high to ultra-high energies.
This paper is concerned with a stochastic model for the spread of an epidemic with a contact tracing scheme, in which diagnosed individuals may name some of their infectious contacts, who are then removed if they have not been already. Traced individuals may or may not also be asked to name their own contacts. The epidemic is studied by considering an approximating, modified birth-death process with intersibling dependencies, for which a threshold parameter and expressions from which extinction probabilities may be calculated are derived. When all individuals can name their contacts, it is shown that this threshold parameter depends on the infectious period distribution only through its mean. Numerical studies show that the infectious period distribution choice can have a material effect on the threshold behaviour of an epidemic, while the dependencies help reduce spread.
The first dedicated space-VLBI project, the VLBI Space Observatory Programme (VSOP), commenced with the successful launch of radio-astronomical satellite HALCA in 1997. Plans for a second generation space-VLBI project have been made by a working group over a number of years. This project, VSOP-2, has now been approved by Japan's space agency, JAXA, as the ASTRO-G project. It is planned for the spacecraft to observe in the 8, 22 and 43 GHz bands with cooled receivers for the two higher bands, which include important maser lines. It will have a maximum angular resolution at 43 GHz (7 mm) of about 40 micro-arcseconds. Although the VSOP project mainly observed continuum emission from active galactic nuclei (AGN), VSOP-2/ASTRO-G is expected to enable a variety of high angular resolution maser line observations.
Writing African History is an essential work for anyone who wants to write, or even seriously read, African history. It will replace Daniel McCall's classic Africa in Time Perspective as the introduction to African history for the next generation and as a reference for professional historians, interested readers, and anyone who wants to understand how African history is written. Africa in Time Perspective was written in the 1960s, when African history was a new field of research. This new book reflects the development of African history since then. It opens with a comprehensive introduction by Daniel McCall, followed by a chapter by the editor explaining what African history is [and is not] in the context of historical theory and the development of historical narrative, the humanities, and social sciences. The first half of the book focuses on sources of historical data while the second half examines different perspectives on history. The editor's final chapter explains how to combine various sorts of evidence into a coherent account of African history. Writing African History will become the most important guide to African history for the 21st century.
Contributors: Bala Achi, Isaac Olawale Albert, Diedre L. Badéjo, Dorothea Bedigian, Barbara M. Cooper, Henry John Drewal, Christopher Ehret, Toyin Falola, David Henige, Joseph E. Holloway, John Hunwick, S. O. Y. Keita, William G. Martin, Daniel McCall, Susan Keech McIntosh, Donatien Dibwe Dia Mwembu, Kathleen Sheldon, John Thornton, and Masao Yoshida.
John Edwards Philips is Professor of International Society, Hirosaki University, and author of Spurious Arabic: Hausa and Colonial Nigeria [Madison, University of Wisconsin African Studies Center, 2000].