Markov Chain Monte Carlo Method without Detailed Balance

We present a specific algorithm that generally satisfies the balance condition without imposing the detailed balance in the Markov chain Monte Carlo. In our algorithm, the average rejection rate is minimized, and even reduced to zero in many relevant cases. The absence of the detailed balance also introduces a net stochastic flow in a configuration space, which further boosts up the convergence. We demonstrate that the autocorrelation time of the Potts model becomes more than 6 times shorter than that by the conventional Metropolis algorithm. Based on the same concept, a bounce-free worm algorithm for generic quantum spin models is formulated as well.Comment: 5 pages, 5 figure

Prevalence of infection with human herpesvirus 8/Kaposi's sarcoma herpesvirus in rural South Africa

Objective. To determine prevalence of infection with human herpesvirus 8 (HHV-8)/Kaposi's sarcoma herpesvirus (KSHV) and to gain some insight into possible transmission dynamics of this novel virus in South Africa. Methods. Stored, anonymous serum from 50 patients with a sexually transmitted disease (STD), 50 adult medical ward patients (25 male, 25 female), and 36 paediatric ward patients in Hlabisa Hospital, KwaZulu-Natal, was screened by enzyme-linked immunosorbent assay (ELISA) for antibodies to the small capsid-related protein encoded by HHV-8/KSHV orf65. Antibodies to the latency-associated nuclear antigen(LANA) were measured by immunofluorescence, and sera that were reactive in the ELISA but negative by immunofluorescence were re-tested by Western blot against the recombinant orf65 protein to exclude nonspecific reactivity. Results. Overall, 47 patients tested positive (34.6%), 76 tested negative (55.9%) and 13 (9.5%) had indeterminate results. Among those wit a definite result, prevalence was similar among males (47.2%) and females (52.8%) and increased in later adulthood (<18 months 37.5%, 19 - 120 months 38.5%, 15 - 34 years 32.1% 35 - 69 years 62.8%). Prevalence was highest among medical patients (58.1%); among those with with an STD it was 31.1% (P = 0.01), and among children it was 22.8% (P = 0.001). When age-adjusted, prevalence among medical patients (23.7%) was similar to that among patients with an STD. Conclusion. Prevalence of HHV-8/KSHV is high in this setting and transmission appears to be occurring in childhood as well as among adults. Larger population-based studies are required to detail the transmission dynamics of HHSV-8/KSHV.4 page(s

A Bayesian approach to the follow-up of candidate gravitational wave signals

Ground-based gravitational wave laser interferometers (LIGO, GEO-600, Virgo and Tama-300) have now reached high sensitivity and duty cycle. We present a Bayesian evidence-based approach to the search for gravitational waves, in particular aimed at the followup of candidate events generated by the analysis pipeline. We introduce and demonstrate an efficient method to compute the evidence and odds ratio between different models, and illustrate this approach using the specific case of the gravitational wave signal generated during the inspiral phase of binary systems, modelled at the leading quadrupole Newtonian order, in synthetic noise. We show that the method is effective in detecting signals at the detection threshold and it is robust against (some types of) instrumental artefacts. The computational efficiency of this method makes it scalable to the analysis of all the triggers generated by the analysis pipelines to search for coalescing binaries in surveys with ground-based interferometers, and to a whole variety of signal waveforms, characterised by a larger number of parameters.Comment: 9 page

Using Markov chain Monte Carlo methods for estimating parameters with gravitational radiation data

We present a Bayesian approach to the problem of determining parameters for coalescing binary systems observed with laser interferometric detectors. By applying a Markov Chain Monte Carlo (MCMC) algorithm, specifically the Gibbs sampler, we demonstrate the potential that MCMC techniques may hold for the computation of posterior distributions of parameters of the binary system that created the gravity radiation signal. We describe the use of the Gibbs sampler method, and present examples whereby signals are detected and analyzed from within noisy data.Comment: 21 pages, 10 figure

Costs and cost-effectiveness of alternative tuberculosis management strategies in South Africa - Implications for policy

Objective. To conduct an economic analysis of the Hlabisa community-based directly observed therapy management strategy for tuberculosis and to project costs of three alternative strategies. Setting. Hlabisa health district, KwaZulu-Natal, South Africa. Methods. An economic analysis comparing the current tuberculosis management strategy in Hlabisa with three alternative strategies (the Hlabisa strategy prior to 1991 based on hospitalisation, the national strategy and sanatorium care) in terms of costs to both health service and patient and of cost-effectiveness. Results. The current Hlabisa strategy was the most cost-effective (R3 799 per patient cured), compared with R98 307 for the strategy used prior to 1991, R9 940 for the national strategy, and R11 145 for sanatorium care, Between 71% and 88% of treatment costs lie with the health service, and hospitalisation (R119 per day) is the most expensive item. Prolonged hospitalisation is extremely expensive, but community care is cheaper (community clinic visit, R28; community health worker visit, R7). The total cost of supervising a patient in the community under the current Hlabisa strategy was R503, equivalent to 4.2 days in hospital, Drug costs (R157) are equivalent to just 1.3 days in hospital. Conclusion. Cost to both health service and patient can be substantially reduced by using community-based directly observed therapy for tuberculosis, a strategy that is cheap and cost-effective in Hlabisa, These findings have important national implications, supporting the goals of the new tuberculosis control programme.5 page(s

Direct reconstruction of the quintessence potential

We describe an algorithm which directly determines the quintessence potential from observational data, without using an equation of state parametrisation. The strategy is to numerically determine observational quantities as a function of the expansion coefficients of the quintessence potential, which are then constrained using a likelihood approach. We further impose a model selection criterion, the Bayesian Information Criterion, to determine the appropriate level of the potential expansion. In addition to the potential parameters, the present-day quintessence field velocity is kept as a free parameter. Our investigation contains unusual model types, including a scalar field moving on a flat potential, or in an uphill direction, and is general enough to permit oscillating quintessence field models. We apply our method to the `gold' Type Ia supernovae sample of Riess et al. (2004), confirming the pure cosmological constant model as the best description of current supernovae luminosity-redshift data. Our method is optimal for extracting quintessence parameters from future data.Comment: 9 pages RevTeX4 with lots of incorporated figure

Testing for double inflation with WMAP

With the WMAP data we can now begin to test realistic models of inflation involving multiple scalar fields. These naturally lead to correlated adiabatic and isocurvature (entropy) perturbations with a running spectral index. We present the first full (9 parameter) likelihood analysis of double inflation with WMAP data and find that despite the extra freedom, supersymmetric hybrid potentials are strongly constrained with less than 7% correlated isocurvature component allowed when standard priors are imposed on the cosomological parameters. As a result we also find that Akaike & Bayesian model selection criteria rather strongly prefer single-field inflation, just as equivalent analysis prefers a cosmological constant over dynamical dark energy in the late universe. It appears that simplicity is the best guide to our universe.Comment: 7 pages, 6 figure

Risk Factors for High Early Mortality in Patients on Antiretroviral Treatment in a Rural District of Malawi.

OBJECTIVES: Among adults started on antiretroviral treatment (ART) in a rural district hospital (a) to determine the cumulative proportion of deaths that occur within 3 and 6 months of starting ART, and (b) to identify risk factors that may be associated with such mortality. DESIGN AND SETTING: A cross-sectional analytical study set in Thyolo district, Malawi. METHODS: Over a 2-year period (April 2003 to April 2005) mortality within the first 3 and 6 months of starting ART was determined and risk factors were examined. RESULTS: A total of 1507 individuals (517 men and 990 women), whose median age was 35 years were included in the study. There were a total of 190 (12.6%) deaths on ART of which 116 (61%) occurred within the first 3 months (very early mortality) and 150 (79%) during the first 6 months of initiating ART. Significant risk factors associated with such mortality included WHO stage IV disease, a baseline CD4 cell count under 50 cells/mul and increasing grades of malnutrition. A linear trend in mortality was observed with increasing grades of malnutrition (chi for trend = 96.1, P </= 0.001) and decreasing CD4 cell counts (chi for trend = 72.4, P </= 0.001). Individuals who were severely malnourished [body mass index (BMI) < 16.0 kg/m] had a six times higher risk of dying in the first 3 months than those with a normal nutritional status. CONCLUSIONS: Among individuals starting ART, the BMI and clinical staging could be important screening tools for use to identify and target individuals who, despite ART, are still at a high risk of early death