The inevitable youthfulness of known high-redshift radio galaxies

Radio galaxies can be seen out to very high redshifts, where in principle they can serve as probes of the early evolution of the Universe. Here we show that for any model of radio-galaxy evolution in which the luminosity decreases with time after an initial rapid increase (that is, essentially all reasonable models), all observable high-redshift radio-galaxies must be seen when the lobes are less than 10^7 years old. This means that high-redshift radio galaxies can be used as a high-time-resolution probe of evolution in the early Universe. Moreover, this result helps to explain many observed trends of radio-galaxy properties with redshift [(i) the `alignment effect' of optical emission along radio-jet axes, (ii) the increased distortion in radio structure, (iii) the decrease in physical sizes, (iv) the increase in radio depolarisation, and (v) the increase in dust emission] without needing to invoke explanations based on cosmology or strong evolution of the surrounding intergalactic medium with cosmic time, thereby avoiding conflict with current theories of structure formation.Comment: To appear in Nature. 4 pages, 2 colour figures available on request. Also available at http://www-astro.physics.ox.ac.uk/~km

Willingness to participate in future HIV prevention studies among gay and bisexual men in Scotland, UK: a challenge for intervention trials

This article examines willingness to participate in future HIV prevention research among gay and bisexual men in Scotland, UK. Anonymous, self-complete questionnaires and Orasure Gäó oral fluid samples were collected in commercial gay venues. 1,320 men were eligible for inclusion. 78.2% reported willingness to participate in future HIV prevention research; 64.6% for an HIV vaccine, 57.4% for a behaviour change study, and 53.0% for a rectal microbicide. In multivariate analysis, for HIV vaccine research, greater age, minority ethnicity, and not providing an oral fluid sample were associated with lower willingness; heterosexual orientation and not providing an oral fluid sample were for microbicides; higher education and greater HIV treatment optimism were for behaviour change. STI testing remained associated with being more willing to participate in microbicide research and frequent gay scene use remained associated with being more willing to participate in behaviour change research. Having an STI in the past 12 months remained significantly associated with being willing to participate in all three study types. There were no associations between sexual risk behaviour and willingness. Although most men expressed willingness to participate in future research, recruitment of high-risk men, who have the potential to benefit most, is likely to be more challenging

Modern tests of Lorentz invariance

Motivated by ideas about quantum gravity, a tremendous amount of effort over the past decade has gone into testing Lorentz invariance in various regimes. This review summarizes both the theoretical frameworks for tests of Lorentz invariance and experimental advances that have made new high precision tests possible. The current constraints on Lorentz violating effects from both terrestrial experiments and astrophysical observations are presented.Comment: Modified and expanded discussions of various points. Numerous references added. Version matches that accepted by Living Reviews in Relativit

Varying constants, Gravitation and Cosmology

Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. It is thus of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We thus detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit

What constitutes the best sex life for gay and bisexual men? Implications for HIV prevention.

BACKGROUND: While a large body of research has sought to understand HIV transmission risk behaviours among gay men, bisexual men and other men who have sex with men (MSM), less attention has been paid to the wider sexual health and well-being of this population. While some community-based organisations aim to support a more holistic sense of sexual well-being there is little evidence to draw on to inform their interventions. The current study sought to explore gay and bisexual men's conceptions of what constitutes the 'best sex'. METHOD: The EMIS survey of 2010 recruited more than 180,000 respondents from 38 European countries to complete an online questionnaire about sexual health and behaviour. The 12,942 English language, UK-based responses to the open ended question, "What's your idea of the best sex life?" were subjected to a detailed content analysis. A framework was devised to reflect and describe the key themes emerging from the data, which was then used to code all responses to one (or more) of these themes. Further statistical analysis sought to establish if and how responses differed according to key demographic variables. RESULTS: Eight themes emerged that capture the diversity of gay and bisexual men's sexual desires. Most common among responses was a desire for sex within committed relationships, followed by a desire for sex which is emotionally or psychologically connected. Men also expressed a desire for volume and variety in their sexual lives, and for sex that is free from physical, social or psychological harm. Comparative analysis identified that older men were less likely to idealise a relationship or emotional connection, but were more likely to specify the sexual acts or behaviours they wished to engage in. CONCLUSIONS: Attending to what men value or aspire to can help ensure interventions are engaging and meaningful to the target population. HIV prevention interventions need to attend to the broad range of sexual desires held by gay and bisexual men in delivery of holistic sexual health promotion that can help them to have the best sex with the least harm