A Young Planetary-Mass Object in the ρ Oph Cloud Core

We report the discovery of a young planetary-mass brown dwarf in the ρ Oph cloud core. The object was identified as such with the aid of a 1.5-2.4 μm low-resolution spectrum obtained using the NIRC instrument on the Keck I telescope. Based on the COND model, the observed spectrum is consistent with a reddened (A_V ~ 15-16) brown dwarf whose effective temperature is in the range 1200-1800 K. For an assumed age of 1 Myr, comparison with isochrones further constrains the temperature to ~1400 K and suggests a mass of ~2-3 Jupiter masses. The inferred temperature is suggestive of an early T spectral type, which is supported by spectral morphology consistent with weak methane absorption. Based on its inferred distance (~100 pc) and the presence of overlying visual absorption, it is very likely to be a ρ Oph cluster member. In addition, given the estimated spectral type, it may be the youngest and least massive T dwarf found so far. Its existence suggests that the initial mass function for the ρ Oph star-forming region extends well into the planetary-mass regime

Joseph Chamberlain and South Africa

African Studies Seminar series. Paper presented 4 August 1983The most remarkable feature of Joseph Chamberlains government of the Empire was his attempt to command assent at home and abroad. At home he was extraordinarily successful. His complicity in the Jameson Raid and his responsibility for the long, expensive and no more than marginally successful war with the South African republics made that achievement only the more remarkable. But abroad, particularly in South Africa, success eluded him. That lack of success raised questions about the worth of his whole imperial enterprise, questions to which most people now, historians and laymen alike, would give the same negative answer. Conscious of the risk of failure though equally confident of the possibility of success, Chamberlain concentrated his final energies on an attempt to harness domestic and colonial economic self-interest to the chariot of the Empire, This time success eluded him at home, though he might have been able to turn the tide there if fate had allowed him the same vigorous old age that Gladstone and later Churchill enjoyed. But this part of Chamberlain's story lies outside my concern in this essay. What I want to suggest here is the liberal as well as authoritarian character of his leadership of the Empire particularly in South Africa during his tenure as Colonial Secretary

A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone

This study undertakes a CMIP5 model selection specific to the Winter Rainfall Zone (WRZ) of South Africa, seeking to reduce the range of future climate projections through identifying a subset of models with increased realism and independence. In order to navigate the subjectivity in identifying relevant circulation metrics to assess models against, the ‘Day Zero' drought is used as a characteristic episode. Here initially the extensive literature produced subsequent to the drought has been drawn on to identify and evaluate relevant regional process metrics, before utilising the anomalous conditions during the drought to validate various assessment methods. The dynamics subsequently identified as being most influential to rainfall supply in the WRZ include the South Atlantic subtropical jet stream responsible for steering of mid-latitude storm systems, the South Atlantic subtropical high, and the presence, or preferably absence, of precipitation blocking subsidence, and the prevalence of mid-latitude storm systems, critical for transport and upliftment of moisture to the region. Models were subsequently assessed against these metrics and scored following the technique of McSweeney et al. (2015). Unrealistic models were removed from the ensemble while significantly biased models were also excluded as their absence did not significantly reduce the range of future projections. The same scoring methods were then utilised to create a genealogy of models attaining similar results to that of Knutti, Masson & Gettelman (2013). A subset of 6 CMIP5 models which are more independent and historically more realistic than that of the full ensemble were subsequently identified. While the range of future temperature projections of the final ensemble are somewhat constrained in comparison to the full ensemble, the primary utility is argued to be the reduced number of models where a future researcher may consider each model's projected future climate pathway individually before selecting a model, or models, which best informs their use case, whilst being assured that this model performs suitably well in the region and that the initial ensemble considered adequately represents model uncertainty, while strong similarity between two or more models within the ensemble will not be unduly biasing results

Interactions between actinophage and streptomycetes in soil and the fate of phage-borne genes

Host activity is essential for bacteriophage survival. Bacterial growth in soil is sporadic and discontinuous in time and space. Phages must therefore adopt strategies to overcome periods of host inactivity, such as the lysogenic life-cycle, for long-term survival in soil. KC301 (a derivative of oC31) which contains the thiostrepton resistance gene tsr was inoculated into soil microcosms as a lysate or via lysogenic hosts, together with combinations of Streptomyces spp. populations. Phage and host populations were monitored over periods of incubation of between 12 and 47 days. The possibility of KC301 lysogenizing indigenous streptomycetes in nonsterile soil was investigated by selection for thiostrepton resistance and molecular analysis of lysogen DNA. The effects of selection for phage-borne tsr was examined by adding thiostrepton to soil microcosms before inoculation of soil with resistant lysogenic and sensitive uninfected strains of Streptomyces lividans. Correlation between metabolic activity of S. lividans and infection by KC301 in soil was also assessed. KC301 lysogenized indigenous streptomycetes in nonsterile soil when added as a lysate, but not as a prophage in lysogenic spores. A sample of indigenous lysogens proved to contain integrated KC301 DNA. Most of the isolates were stable lysogens, retaining thiostrepton resistance after several rounds of sub-culturing. Interactions between S. lividans and KC301 in soil were limited by the densities of both host and phage populations. In most cases, host population densities in soil were not reduced by lytic KC301 infections. When reduction by lytic KC301 infections of the mycelial stage occurred in soil, sporulation compensated for loss of total viable propagules. KC301 infected hosts in soil, and established itself as a prophage in lysogenic spores in soil. Turnover of soil at defined times stimulated a small proportion of lysogenic spores to germinate and release KC301 into the soil. KC301 released from germinating lysogenic spores could infect and lysogenize previously uninfected soil inoculants of the same or different Streptomyces spp. Lysogenic populations reached lower levels than those of uninfected counterparts, whether growing in the presence or absence of those counterparts. Thiostrepton in soil caused reduction in the mycelial stage during vegetative growth of sensitive strains following inoculation, but as with phage infections, this was compensated by sporulation. The KC301 lysogen were not affected by thiostrepton in soil, although no selective advantage was conferred on the lysogen population by the presence of the antibiotic. The majority of the KC301 population in soil existed in the prophage state when soil was inoculated with lysogenic hosts. Although lysogenic hosts were competitively compromised, inputs into the free phage pool could occur without further detriment to host density. Sporulation of hosts compensated for killing of mycelium in soil, and facilitated long-term persistence of KC301