The long-wavelength view of GG Tau A: rocks in the ring world

We present the first detection of GG Tau A at centimetre wavelengths, made with the Arcminute Microkelvin Imager Large Array at a frequency of 16 GHz (λ = 1.8 cm). The source is detected at >6 σrms with an integrated flux density of S16GHz = 249 ± 45 µJy. We use these new centimetre-wave data, in conjunction with additional measurements compiled from the literature, to investigate the long-wavelength tail of the dust emission from this unusual protoplanetary system. We use an MCMC-based method to determine maximum likelihood parameters for a simple parametric spectral model and consider the opacity and mass of the dust contributing to the microwave emission. We derive a dust mass of Md ~ 0.1 Msun, constrain the dimensions of the emitting region and find that the opacity index at λ > 7 mm is less than unity, implying a contribution to the dust population from grains exceeding ~4 cm in size. We suggest that this indicates coagulation within the GG Tau A system has proceeded to the point where dust grains have grown to the size of small rocks with dimensions of a few centimetres. Considering the relatively young age of the GG Tau association in combination with the low derived disc mass, we suggest that this system may provide a useful test case for rapid core accretion planet formation models

Multiscale Analysis of the Gradient of Linear Polarisation

We propose a new multiscale method to calculate the amplitude of the gradient of the linear polarisation vector using a wavelet-based formalism. We demonstrate this method using a field of the Canadian Galactic Plane Survey (CGPS) and show that the filamentary structure typically seen in gradients of linear polarisation maps depends strongly on the instrumental resolution. Our analysis reveals that different networks of filaments are present on different angular scales. The wavelet formalism allows us to calculate the power spectrum of the fluctuations seen in gradients of linear polarisation maps and to determine the scaling behaviour of this quantity. The power spectrum is found to follow a power law with gamma ~ 2.1. We identify a small drop in power between scales of 80 < l < 300 arcmin, which corresponds well to the overlap in the u-v plane between the Effelsberg 100-m telescope and the DRAO 26-m telescope data. We suggest that this drop is due to undersampling present in the 26-m telescope data. In addition, the wavelet coefficient distributions show higher skewness on smaller scales than at larger scales. The spatial distribution of the outliers in the tails of these distributions creates a coherent subset of filaments correlated across multiple scales, which trace the sharpest changes in the polarisation vector P within the field. We suggest that these structures may be associated with highly compressive shocks in the medium. The power spectrum of the field excluding these outliers shows a steeper power law with gamma ~ 2.5.Comment: 12 pages, 12 figure

Transfer learning for radio galaxy classification

In the context of radio galaxy classification, most state-of-the-art neural network algorithms have been focused on single survey data. The question of whether these trained algorithms have cross-survey identification ability or can be adapted to develop classification networks for future surveys is still unclear. One possible solution to address this issue is transfer learning, which re-uses elements of existing machine learning models for different applications. Here we present radio galaxy classification based on a 13-layer Deep Convolutional Neural Network (DCNN) using transfer learning methods between different radio surveys. We find that our machine learning models trained from a random initialization achieve accuracies comparable to those found elsewhere in the literature. When using transfer learning methods, we find that inheriting model weights pre-trained on FIRST images can boost model performance when re-training on lower resolution NVSS data, but that inheriting pre-trained model weights from NVSS and re-training on FIRST data impairs the performance of the classifier. We consider the implication of these results in the context of future radio surveys planned for next-generation radio telescopes such as ASKAP, MeerKAT, and SKA1-MID

Testing protoplanetary disc dispersal with radio emission

We consider continuum free-free radio emission from the upper atmosphere of protoplanetary discs as a probe of the ionized luminosity impinging upon the disc. Making use of previously computed hydrodynamic models of disc photoevaporation within the framework of EUV and X-ray irradiation, we use radiative transfer post-processing techniques to predict the expected free-free emission from protoplanetary discs. In general, the free-free luminosity scales roughly linearly with ionizing luminosity in both EUV and X-ray driven scenarios, where the emission dominates over the dust tail of the disc and is partial optically thin at cm wavelengths. We perform a test observation of GM Aur at 14-18 Ghz and detect an excess of radio emission above the dust tail to a very high level of confidence. The observed flux density and spectral index are consistent with free-free emission from the ionized disc in either the EUV or X-ray driven scenario. Finally, we suggest a possible route to testing the EUV and X-ray driven dispersal model of protoplanetary discs, by combining observed free-free flux densities with measurements of mass-accretion rates. On the point of disc dispersal one would expect to find a M_dot^2 scaling with free-free flux in the case of EUV driven disc dispersal or a M_dot scaling in the case of X-ray driven disc dispersal.Comment: Accepted MNRAS, 12 pages, 11 figures, (pdf generation fixed

Social Networks as the New Frontier of Terrorism

Terrorism. Why does this word grab our attention so? Propaganda machines have adopted modern technology as a means to always have their content available. Regardless of the hour or time zone, information is being shared by somebody, somewhere. Social media is a game changer influencing the way in which terror groups are changing their tactics and also how their acts of terror are perceived by the members of the public they intend to influence. This book explores how social media adoption by terrorists interacts with privacy law, freedom of expression, data protection and surveillance legislation through an exploration of the fascinating primary resources themselves, covering everything from the Snowden Leaks, the rise of ISIS to Charlie Hebdo. The book also covers lesser worn paths such as the travel guide that proudly boasts that you can get Bounty and Twix bars mid-conflict, and the best local hair salons for jihadi brides. These vignettes, amongst the many others explored in this volume bring to life the legal, policy and ethical debates considered in this volume, representing an important part in the development of understanding terrorist narratives on social media, by framing the legislative debate. This book represents an invaluable guide for lawyers, government bodies, the defence services, academics, students and businesses

Using "tangibles" to promote novel forms of playful learning

Tangibles, in the form of physical artefacts that are electronically augmented and enhanced to trigger various digital events to happen, have the potential for providing innovative ways for children to play and learn, through novel forms of interacting and discovering. They offer, too, the scope for bringing playfulness back into learning. To this end, we designed an adventure game, where pairs of children have to discover as much as they can about a virtual imaginary creature called the Snark, through collaboratively interacting with a suite of tangibles. Underlying the design of the tangibles is a variety of transforms, which the children have to understand and reflect upon in order to make the Snark come alive and show itself in a variety of morphological and synaesthesic forms. The paper also reports on the findings of a study of the Snark game and discusses what it means to be engrossed in playful learning

Limits on the validity of the thin-layer model of the ionosphere for radio interferometric calibration

For a ground-based radio interferometer observing at low frequencies, the ionosphere causes propagation delays and refraction of cosmic radio waves which result in phase errors in the received signal. These phase errors can be corrected using a calibration method that assumes a two-dimensional phase screen at a fixed altitude above the surface of the Earth, known as the thin-layer model. Here we investigate the validity of the thin-layer model and provide a simple equation with which users can check when this approximation can be applied to observations for varying time of day, zenith angle, interferometer latitude, baseline length, ionospheric electron content and observing frequency.Comment: 8 pages, 10 figures, accepted MNRA

Ecological resources within Advaita Vedanta

The world, in which we live, stands at a precipice. Ecological disasters now threaten the very existence of human civilization. The so called shallow\u27 environmental initiatives that continue to dominate the political and social landscape have proved ineffective in dealing with this problem. It is crucial that all of humanity actively embrace radical change in regards to how we go about our lives. No where is this more apparent than in the Indian subcontinent. Two radical ecologies that have emerged from the West, Deep Ecology and Social Ecology, offer a vision as to the nature of that change. This document examines Advaita Vedanta, the dominant form of Hinduism, in order to identify those aspects of the religion that facilitate radical ecological change among believers. Activists working in the subcontinent can then utilize these aspects of Advaita to engage the Indian population regarding ecological matters in a Hindu way