Galaxy Zoo: Passive Red Spirals

We study the spectroscopic properties and environments of red spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on, disk dominated spirals we construct a sample of truly passive disks (not dust reddened, nor dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spirals and red early types. We use SDSS data to investigate the physical processes which could have turned these objects red without disturbing their morphology. Red spirals prefer intermediate density regimes, however there are no obvious correlations between red spiral properties and environment - environment alone is not sufficient to determine if a spiral will become red. Red spirals are a small fraction of spirals at low masses, but are a significant fraction at large stellar masses - massive galaxies are red independent of morphology. We confirm that red spirals have older stellar popns and less recent star formation than the main spiral population. While the presence of spiral arms suggests that major star formation cannot have ceased long ago, we show that these are not recent post-starbursts, so star formation must have ceased gradually. Intriguingly, red spirals are ~4 times more likely than normal spirals to host optically identified Seyfert or LINER, with most of the difference coming from LINERs. We find a curiously large bar fraction in the red spirals suggesting that the cessation of star formation and bar instabilities are strongly correlated. We conclude by discussing the possible origins. We suggest they may represent the very oldest spiral galaxies which have already used up their reserves of gas - probably aided by strangulation, and perhaps bar instabilities moving material around in the disk.Comment: MNRAS in press, 20 pages, 15 figures (v3

Genomic epidemiology of SARS-CoV-2 in a UK university identifies dynamics of transmission

AbstractUnderstanding SARS-CoV-2 transmission in higher education settings is important to limit spread between students, and into at-risk populations. In this study, we sequenced 482 SARS-CoV-2 isolates from the University of Cambridge from 5 October to 6 December 2020. We perform a detailed phylogenetic comparison with 972 isolates from the surrounding community, complemented with epidemiological and contact tracing data, to determine transmission dynamics. We observe limited viral introductions into the university; the majority of student cases were linked to a single genetic cluster, likely following social gatherings at a venue outside the university. We identify considerable onward transmission associated with student accommodation and courses; this was effectively contained using local infection control measures and following a national lockdown. Transmission clusters were largely segregated within the university or the community. Our study highlights key determinants of SARS-CoV-2 transmission and effective interventions in a higher education setting that will inform public health policy during pandemics.</jats:p

Facebook or Fakebook? : The effects of simulated mobile applications on simulated mobile networks

This work was supported by the Engineering and Physical Sciences Research Council [grant number EP/G002606/1].The credibility of mobile ad hoc network simulations depends on accurate characterisations of user behaviour, e.g., mobility and application usage. If simulated nodes communicate at different rates to real nodes, or move in an unrealistic fashion, this may have a large impact on the network protocols being simulated and tested. Many future mobile network protocols, however, may also depend on future mobile applications. Different applications may be used at different rates or in different manners. But how can we determine realistic user behaviour for such applications that do not yet exist? One common solution is again simulation, but this time simulation of these future applications. This paper examines differences in user behaviour between a real and simulated mobile social networking application through a user study (n=80). We show that there are distinct differences in privacy behaviour between the real and simulated groups. We then simulate a mobile opportunistic network application using two real-world traces to demonstrate the impact of using real and simulated applications. We find large differences between using real and synthetic models of privacy behaviour, but smaller differences between models derived from the real and simulated applications.PostprintPeer reviewe