South African national household survey of HIV/AIDS prevalence, behavioural risks and mass media impact-detailed methodology and response rate results

Objectives. To describe the methodology used in a recent survey of HIV/AIDS in South Africa and to present the response rates.Methods. A cross-sectional, national household-based survey was conducted using second-generation surveillance procedures. A complex multistage sampling technique was used to create a master sample of 1 000 census enumerator areas out of a total of 86 000 nationally. Aerial photographs were taken and used to randomly select more than 10 197 households and ultimately 13 518 individuals from a sampling frame of 31 321 people. Phase 1 of the study involved notifying the household residents about the study and collecting key demographic information on respondents aged 2 years and older. This information was used to randomly select up to 3 respondents from each household: 1 adult (25 years and older), 1 youth (15- 24 years), and 1 child (2- 14 years). In phase 2 nurses interviewed respondents and collected oral fluid specimens for HIV testing. In the case of children aged 2 - 11 years, parents or guardians were interviewed, but HIV testing was performed on the selected children. Questionnaire data were anonymously linked with HIV test results.Results. A total of 9 963 persons agreed to be interviewed and 8 840 were tested for HIV, yielding a response rate of 73.7% and 65.4% respectively. However, only 8 428 (62.3%) HIV test results were correctly matched with behavioural data. The results showed that those tested for HIV did not differ from those not tested in terms of key determinants.Conclusion. It is possible to use community-based surveys to study the prevalence of HIV in the general population

The time to extinction for an SIS-household-epidemic model

We analyse a stochastic SIS epidemic amongst a finite population partitioned into households. Since the population is finite, the epidemic will eventually go extinct, i.e., have no more infectives in the population. We study the effects of population size and within household transmission upon the time to extinction. This is done through two approximations. The first approximation is suitable for all levels of within household transmission and is based upon an Ornstein-Uhlenbeck process approximation for the diseases fluctuations about an endemic level relying on a large population. The second approximation is suitable for high levels of within household transmission and approximates the number of infectious households by a simple homogeneously mixing SIS model with the households replaced by individuals. The analysis, supported by a simulation study, shows that the mean time to extinction is minimized by moderate levels of within household transmission

Entanglement in the quantum Ising model

We study the asymptotic scaling of the entanglement of a block of spins for the ground state of the one-dimensional quantum Ising model with transverse field. When the field is sufficiently strong, the entanglement grows at most logarithmically in the number of spins. The proof utilises a transformation to a model of classical probability called the continuum random-cluster model, and is based on a property of the latter model termed ratio weak-mixing. Our proof applies equally to a large class of disordered interactions

Numerical Study of a Field Theory for Directed Percolation

A numerical method is devised for study of stochastic partial differential equations describing directed percolation, the contact process, and other models with a continuous transition to an absorbing state. Owing to the heightened sensitivity to fluctuationsattending multiplicative noise in the vicinity of an absorbing state, a useful method requires discretization of the field variable as well as of space and time. When applied to the field theory for directed percolation in 1+1 dimensions, the method yields critical exponents which compare well against accepted values.Comment: 18 pages, LaTeX, 6 figures available upon request LC-CM-94-00

Phase Transitions on Nonamenable Graphs

We survey known results about phase transitions in various models of statistical physics when the underlying space is a nonamenable graph. Most attention is devoted to transitive graphs and trees

TRAPUM discovery of thirteen new pulsars in NGC 1851 using MeerKAT

We report the discovery of 13 new pulsars in the globular cluster NGC 1851 by the TRAPUM Large Survey Project using the MeerKAT radio telescope. The discoveries consist of six isolated millisecond pulsars (MSPs) and seven binary pulsars, of which six are MSPs and one is mildly recycled. For all the pulsars, we present the basic kinematic, astrometric, and orbital parameters, where applicable, as well as their polarimetric properties, when these are measurable. Two of the binary MSPs (PSR J0514-4002D and PSR J0514-4002E) are in wide and extremely eccentric (e > 0.7) orbits with a heavy white dwarf and a neutron star as their companion, respectively. With these discoveries, NGC 1851 is now tied with M28 as the cluster with the third largest number of known pulsars (14). Its pulsar population shows remarkable similarities with that of M28, Terzan 5 and other clusters with comparable structural parameters. The newly-found pulsars are all located in the innermost regions of NGC 1851 and will likely enable, among other things, detailed studies of the cluster structure and dynamics