Coupling Control Variates for Markov Chain Monte Carlo

We show that Markov couplings can be used to improve the accuracy of Markov chain Monte Carlo calculations in some situations where the steady-state probability distribution is not explicitly known. The technique generalizes the notion of control variates from classical Monte Carlo integration. We illustrate it using two models of nonequilibrium transport

The Stuff of Other Worlds

Extraterrestrial material eternally rains down on Earth. Meteorites flare in the night sky. Cosmic rays plow into Earth's atmosphere, creating invisible bursts of secondary particles. These processes began when the Earth formed in the primordial solar system and have continued ever since, indifferent to the exceedingly recent presence of human intelligence. For us to seek out stuff of other worlds, in contrast, takes a great deal of determined ingenuity. First we have to send a spacecraft somewhere else in the solar system. Indigenous material has to be collected and then brought back to Earth without exposure to conditions that might significantly alter it. The material must undergo meaningful scientific analysis. Most important, part of the material is preserved intact for future investigations. Beginning with bringing back Moon rocks, and now moving onward in the form of new missions to capture the hot thin solar wind and cold thin atmosphere of comets, extraterrestrial sample return takes place on the cutting edge of scientific technology. Sample return is also the fulcrum of an energetic debate about how to do planetary science missions. Scientists and engineers are debating whether to rely on remote sensing and in situ analysis, or to plan missions to undertake sample return. The latter is definitely more expensive on a per mission basis, and is usually technologically more challenging. But for an initially high investment of money and technology, bringing the stuff of other worlds back to Earth yields an incomparable return in scientific results

Prediction of sustained harmonic walking in the free-living environment using raw accelerometry data

Objective. Using raw, sub-second level, accelerometry data, we propose and validate a method for identifying and characterizing walking in the free-living environment. We focus on the sustained harmonic walking (SHW), which we define as walking for at least 10 seconds with low variability of step frequency. Approach. We utilize the harmonic nature of SHW and quantify local periodicity of the tri-axial raw accelerometry data. We also estimate fundamental frequency of observed signals and link it to the instantaneous walking (step-to-step) frequency (IWF). Next, we report total time spent in SHW, number and durations of SHW bouts, time of the day when SHW occurred and IWF for 49 healthy, elderly individuals. Main results. Sensitivity of the proposed classification method was found to be 97%, while specificity ranged between 87% and 97% and prediction accuracy between 94% and 97%. We report total time in SHW between 140 and 10 minutes-per-day distributed between 340 and 50 bouts. We estimate the average IWF to be 1.7 steps-per-second. Significance. We propose a simple approach for detection of SHW and estimation of IWF, based on Fourier decomposition. The resulting approach is fast and allows processing of a week-long raw accelerometry data (approx. 150 million measurements) in relatively short time (~half an hour) on a common laptop computer (2.8 GHz Intel Core i7, 16 GB DDR3 RAM)

Trends and measurement of HIV prevalence in northern Malawi.

BACKGROUND: Most data on HIV prevalence in Malawi come from antenatal clinic (ANC) surveillance and are, therefore, subject to bias. OBJECTIVES: HIV prevalence and risk factors were measured using population-based data to assess the accuracy of ANC surveillance and changes in prevalence and risk factors for HIV over time. METHODS: HIV prevalence was measured in 1988-1993 and 1998-2001 in community controls from case-control studies of mycobacterial disease in Karonga District, Malawi. ANC surveillance studies in the district began in 1999. RESULTS: Age and area-standardized HIV prevalence in women aged 15-49 years in the community was 3.9% in 1988-1990, 12.5% in 1991-1993 and 13.9% in 1998-2001. For men, HIV prevalence was 3.7%, 9.2% and 11.4% in the same periods. In 1988-1993, HIV positivity was associated with occupations other than farming, with increased schooling and being born outside Karonga District. In 1998-2001, non-farmers were still at higher risk but the other associations were not seen. The age- and area-adjusted HIV prevalence in the ANC in 1999-2001 was 9.2%. The underestimate can be explained largely by marriage and mobility. Reduced fertility in HIV-positive individuals was demonstrated in both ANC and community populations. A previously recommended parity-based adjustment gave an estimated female HIV prevalence of 15.0%. CONCLUSIONS: HIV prevalence has increased and continues to be higher in non-farmers. The increase is particularly marked in those with no education. ANC surveillance underestimated HIV prevalence in the female population in all but the youngest age group. Although there were differences in sociodemographic factors, a parity-based adjustment gave a reasonable estimate of female HIV prevalence

Evaluating the impacts of refuge width on source-sink dynamics between transgenic and non-transgenic cotton

Resistance management for Bt-transgenic crops relies in part on the production of sufficient numbers of susceptible insects in non-toxic refuges. Simulation models suggested that source-sink dynamics could interact with the structure of refuges to impact the production of insects in these areas. We tested the hypothesis that altering isolation between refuges and transgenic cotton by manipulating the width of refuges embedded within cotton fields would alter the density of Heliothis virescens and Helicoverpa zea eggs oviposited in refuges. Three categories of refuge widths were tested over two years: they included narrow (16–24m wide), medium (32-48m wide) and wide (80–96m wide) refuges. Isolation between the two habitats increased as refuge width increased. In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased. In 1997, eggs from H. virescens were analyzed separately from H. zea using an ELISA test. The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge. In contrast, there was no impact of refuge width on the density of H. zea eggs, nor was the slope of a regression of egg density and distance from the refuge significantly different from zero. We suggest that these differences reflect differences in the biology of the two insects

Research to stop tobacco deaths

In 2003, governments adopted the Framework Convention on Tobacco Control, the world’s first global health treaty. In the decade since the treaty was adopted by 178 member states of the World Health Organization, there have been substantial achievements in reducing tobacco use around the world. Research and evidence on the impact of interventions and policies have helped drive this policy progress. An increased and sustained focus on research is needed in the future to ensure that the gains of the global tobacco control movement are maintained, particularly in low- and middle-income countries, which are affected most strongly by the tobacco epidemic. In addition to current priorities, greater attention is needed to research related to trade agreements, prevention among girls, and the appropriate response to nicotine-based noncombustibles (including e-cigarettes)

A Membrane-Organic Phase Oxidation Process for the Destruction of Toxic Organics in Hazardous Wastewaters

The examination of the extraction/oxidation of organic solutes in a two phase oxidation process was undertaken to discern the important parameters and the process mechanism of this system. Several parameter were adjusted to measure their effect on the disappearance rate of each organic from the water phase. The water to PFD volume ratio proved to be the most sensitive parameter affecting the disappearance rate, although temperature was also significant. Comparison with one phase oxidation systems demonstrated that the water/PFD system improved on the reduction of organics from the water phase. B-napthol oxidation increased over 50% in a 2/6 water/PFD volume ratio compared with the water phase oxidation. Phenol, which had the smallest distribution coefficient of the three organics tested, showed a significant reduction rate in the two phase system which was greater than a water phase oxidation system operating at higher pressures. Napthalene and H-coal wastewater also showed more oxidation in the two phase system than in a single water phase system. These results show that two-phase oxidation is a viable process and testing of the total membrane-oxidation system is in order. The feasibility of membrane concentration step is also demonstrated with model organics and actual wastewaters

Children as experiencers: increasing engagement, participation and inclusion for young children in the museum

This research aimed to evaluate young children’s engagement, participation and inclusion within a city museum by utilising observations and semi structured interviews with children and families. Both groups requested more interactive exhibits, sensory experiences, making and doing activities and role play opportunities. In this article, we argue for increased visibility of children’s ‘intangible heritage’(Brookshaw, 2016) and opportunities for responding which make links with children’s lives contemporarily. We further argue that museums should view children as experiencers rather than learners

Different Methods of Balancing Covariates Leading to Different Effect Estimates in the Presence of Effect Modification

A number of covariate-balancing methods, based on the propensity score, are widely used to estimate treatment effects in observational studies. If the treatment effect varies with the propensity score, however, different methods can give very different answers. The authors illustrate this effect by using data from a United Kingdom–based registry of subjects treated with anti–tumor necrosis factor drugs for rheumatoid arthritis. Estimates of the effect of these drugs on mortality varied from a relative risk of 0.4 (95% confidence interval: 0.16, 0.91) to a relative risk of 1.3 (95% confidence interval: 0.8, 2.25), depending on the balancing method chosen. The authors show that these differences were due to a combination of an interaction between propensity score and treatment effect and to differences in weighting subjects with different propensity scores. Thus, the methods are being used to calculate average treatment effects in populations with very different distributions of effect-modifying variables, resulting in different overall estimates. This phenomenon highlights the importance of careful selection of the covariate-balancing method so that the overall estimate has a meaningful interpretation