The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 AU heliocentric distance range inbound

Context. The ESA Rosetta spacecraft, currently orbiting around cornet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. Aims. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. Methods. A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from. Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. Results. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is alpha = -3, instead of alpha = -2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.

Taboo Language and Illness Online: The Use of Specific Emoticons and Graphic Signs to Talk about HIV/AIDS in South Africa

South Africa is one of the countries most affected by HIV/AIDS: According to 2014 UNAIDS data 6.8 million South Africans live with HIV/AIDS, which means a 18.9% prevalence rate among adults (15-49 years old). Despite this strong presence of HIV/AIDS in South African society it remains relatively stigmatized and is not openly talked about. The silence about HIV/AIDS maintained in everyday conversations and the superstitions associated with this illness have led to the creation of a taboo language. This study aims at shedding light on how South African users resort to specific emoticons and graphic signs to talk about HIV/AIDS online. For this purpose 368 Facebook status updates and comments concerning HIV/AIDS and its side effects were analysed. All participants, aged 14-48, lived at the moment of data collection in Cape Town, in the Cape Flats area. The online conversations investigated are mainly in English mixed with Afrikaans and/or Xhosa. The emoticons and graphic signs in most cases display a graphic depiction of the physical (and mental) effects of the illness. These linguistic and semiotic practices employed on Facebook provide insight into how Capetonian users, on the one hand, express solidarity and sympathy with people suffering from HIV/AIDS. On the other hand, the emoticons and graphic signs are used to label and position people affected by HIV/AIDS. Thus, in the South African context social network sites have become an important space and means for communicating HIV/AIDS issues.