Electron trajectories associated with laser-driven coherent synchrotron emission at the front surface of overdense plasmas.

We present an in-depth analysis of an ultrafast electron trajectory type that produces attosecond electromagnetic pulses in both the reflected and forward directions during normal incidence, relativistic laser-plasma interactions. Our particle-in-cell simulation results show that for a target which is opaque to the frequency of the driving laser pulse the emission trajectory is synchrotronlike but differs significantly from the previously identified figure-eight type which produces bright attosecond bursts exclusively in the reflected direction. The origin and characteristics of this trajectory type are explained in terms of the driving electromagnetic fields, the opacity of the plasma, and the conservation of canonical momentum.

Mass deworming for soil-transmitted helminths and schistosomiasis among pregnant women: A systematic review and individual participant data meta-analysis.

The objective of the review is to use individual participant data (IPD) meta-analysis to explore the effect of mass deworming during pregnancy. We developed a search strategy and searched the databases till March 2018. We included individually randomised controlled trials; cluster randomised controlled trials and quasi randomised studies providing preventive or therapeutic deworming drugs for soil transmitted helminthiases and schistosomiasis during pregnancy. All IPD were assessed for completeness, compared to published reports and entered into a common data spreadsheet. Out of the seven trials elgible for IPD, we received data from three trials; out of 8,515 potential IPD participants; data were captured for 5,957 participants. Findings from this IPD suggest that mass deworming during pregnancy reduces maternal anaemia by 23% (Risk ratio [RR]: 0.77, 95% confidence intreval [CI]: 0.73-0.81; three trials; 5,216 participants; moderate quality evidence). We did not find any evidence of an effect of mass deworming during pregnancy on any of the other outcomes. There was no evidence of effect modification; however these findings should be interpreted with caution due to small sample sizes. The quality of evidence was rated as moderate for our findings. Our analyses suggest that mass deworming during pregnancy is associated with reducing anaemia with no evidence of impact on any other maternal or pregnancy outcomes. Our analyses were limited by the availability of data for the impact by subgroups and effect modification. There is also a need to support and promote open data for future IPDs.

Distance to care, care seeking and child mortality in rural Burkina Faso: findings from a population-based cross-sectional survey.

OBJECTIVE: Although distance has been identified as an important barrier to care, evidence for an effect of distance to care on child mortality is inconsistent. We investigated the association of distance to care with self-reported care seeking behaviours, neonatal and post-neonatal under-five child mortality in rural areas of Burkina Faso. METHODS: We performed a cross-sectional survey in 14 rural areas from November 2014 to March 2015. About 100 000 women were interviewed on their pregnancy history and about 5000 mothers were interviewed on their care seeking behaviours. Euclidean distances to the closest facility were calculated. Mixed-effects logistic and Poisson regressions were used respectively to compute odds ratios for care seeking behaviours and rate ratios for child mortality during the 5 years prior to the survey. RESULTS: Thirty per cent of the children lived more than 7 km from a facility. After controlling for confounding factors, there was a strong evidence of a decreasing trend in care seeking with increasing distance to care (P ≤ 0.005). There was evidence for an increasing trend in early neonatal mortality with increasing distance to care (P = 0.028), but not for late neonatal mortality (P = 0.479) and post-neonatal under-five child mortality (P = 0.488). In their first week of life, neonates living 7 km or more from a facility had an 18% higher mortality rate than neonates living within 2 km of a facility (RR = 1.18; 95%CI 1.00, 1.39; P = 0.056). In the late neonatal period, despite the lack of evidence for an association of mortality with distance, it is noteworthy that rate ratios were consistent with a trend and similar to or larger than estimates in early neonatal mortality. In this period, neonates living 7 km or more from a facility had an 18% higher mortality rate than neonates living within 2 km of a facility (RR = 1.18; 95%CI 0.92, 1.52; P = 0.202). Thus, the lack of evidence may reflect lower power due to fewer deaths rather than a weaker association. CONCLUSION: While better geographic access to care is strongly associated with increased care seeking in rural Burkina Faso, the impact on child mortality appears to be marginal. This suggests that, in addition to improving access to services, attention needs to be paid to quality of those services.

Estimating the birth prevalence and pregnancy outcomes of congenital malformations worldwide.

Congenital anomaly registries have two main surveillance aims: firstly to define baseline epidemiology of important congenital anomalies to facilitate programme, policy and resource planning, and secondly to identify clusters of cases and any other epidemiological changes that could give early warning of environmental or infectious hazards. However, setting up a sustainable registry and surveillance system is resource-intensive requiring national infrastructure for recording all cases and diagnostic facilities to identify those malformations that that are not externally visible. Consequently, not all countries have yet established robust surveillance systems. For these countries, methods are needed to generate estimates of prevalence of these disorders which can act as a starting point for assessing disease burden and service implications. Here, we describe how registry data from high-income settings can be used for generating reference rates that can be used as provisional estimates for countries with little or no observational data on non-syndromic congenital malformations.

Enhanced Laser-Driven Ion Acceleration by Superponderomotive Electrons Generated from Near-Critical-Density Plasma.

We report on the experimental studies of laser driven ion acceleration from a double-layer target where a near-critical density target with a few-micron thickness is coated in front of a nanometer-thin diamondlike carbon foil. A significant enhancement of proton maximum energies from 12 to ∼30 MeV is observed when a relativistic laser pulse impinges on the double-layer target under linear polarization. We attributed the enhanced acceleration to superponderomotive electrons that were simultaneously measured in the experiments with energies far beyond the free-electron ponderomotive limit. Our interpretation is supported by two-dimensional simulation results.

Temporal Structure of Attosecond Pulses from Laser-Driven Coherent Synchrotron Emission.

The microscopic dynamics of laser-driven coherent synchrotron emission transmitted through thin foils are investigated using particle-in-cell simulations. For normal incidence interactions, we identify the formation of two distinct electron nanobunches from which emission takes place each half-cycle of the driving laser pulse. These emissions are separated temporally by 130 as and are dominant in different frequency ranges, which is a direct consequence of the distinct characteristics of each electron nanobunch. This may be exploited through spectral filtering to isolate these emissions, generating electromagnetic pulses of duration ∼70 as.

Noncollinear Polarization Gating of Attosecond Pulse Trains in the Relativistic Regime.

High order harmonics generated at relativistic intensities have long been recognized as a route to the most powerful extreme ultraviolet pulses. Reliably generating isolated attosecond pulses requires gating to only a single dominant optical cycle, but techniques developed for lower power lasers have not been readily transferable. We present a novel method to temporally gate attosecond pulse trains by combining noncollinear and polarization gating. This scheme uses a split beam configuration which allows pulse gating to be implemented at the high beam fluence typical of multi-TW to PW class laser systems. Scalings for the gate width demonstrate that isolated attosecond pulses are possible even for modest pulse durations achievable for existing and planned future ultrashort high-power laser systems. Experimental results demonstrating the spectral effects of temporal gating on harmonic spectra generated by a relativistic laser plasma interaction are shown.

Ion Acceleration Using Relativistic Pulse Shaping in Near-Critical-Density Plasmas.

Ultraintense laser pulses with a few-cycle rising edge are ideally suited to accelerating ions from ultrathin foils, and achieving such pulses in practice represents a formidable challenge. We show that such pulses can be obtained using sufficiently strong and well-controlled relativistic nonlinearities in spatially well-defined near-critical-density plasmas. The resulting ultraintense pulses with an extremely steep rising edge give rise to significantly enhanced carbon ion energies consistent with a transition to radiation pressure acceleration.

Causal mediation analysis with multiple mediators.

In diverse fields of empirical research-including many in the biological sciences-attempts are made to decompose the effect of an exposure on an outcome into its effects via a number of different pathways. For example, we may wish to separate the effect of heavy alcohol consumption on systolic blood pressure (SBP) into effects via body mass index (BMI), via gamma-glutamyl transpeptidase (GGT), and via other pathways. Much progress has been made, mainly due to contributions from the field of causal inference, in understanding the precise nature of statistical estimands that capture such intuitive effects, the assumptions under which they can be identified, and statistical methods for doing so. These contributions have focused almost entirely on settings with a single mediator, or a set of mediators considered en bloc; in many applications, however, researchers attempt a much more ambitious decomposition into numerous path-specific effects through many mediators. In this article, we give counterfactual definitions of such path-specific estimands in settings with multiple mediators, when earlier mediators may affect later ones, showing that there are many ways in which decomposition can be done. We discuss the strong assumptions under which the effects are identified, suggesting a sensitivity analysis approach when a particular subset of the assumptions cannot be justified. These ideas are illustrated using data on alcohol consumption, SBP, BMI, and GGT from the Izhevsk Family Study. We aim to bridge the gap from "single mediator theory" to "multiple mediator practice," highlighting the ambitious nature of this endeavor and giving practical suggestions on how to proceed.

Bright subcycle extreme ultraviolet bursts from a single dense relativistic electron sheet.

Double-foil targets separated by a low density plasma and irradiated by a petawatt-class laser are shown to be a copious source of coherent broadband radiation. Simulations show that a dense sheet of relativistic electrons is formed during the interaction of the laser with the tenuous plasma between the two foils. The coherent motion of the electron sheet as it transits the second foil results in strong broadband emission in the extreme ultraviolet, consistent with our experimental observations.

Dust-acoustic shocks in strongly coupled dusty plasmas.

Electrostatic dust-acoustic shock waves are investigated in a viscous, complex plasma consisting of dust particles, electrons, and ions. The system is modelled using the generalized hydrodynamic equations, with strong coupling between the dust particles being accounted for by employing the effective electrostatic temperature approach. Using a reductive perturbation method, it is demonstrated that this model predicts the existence of weakly nonlinear dust-acoustic shock waves, arising as solutions to Burgers's equation, in which the nonlinear forces are balanced by dissipative forces, in this case, associated with viscosity. The evolution and stability of dust-acoustic shocks is investigated via a series of numerical simulations, which confirms our analytical predictions on the shock characteristics.

Dependence of laser-driven coherent synchrotron emission efficiency on pulse ellipticity and implications for polarization gating.

The polarization dependence of laser-driven coherent synchrotron emission transmitted through thin foils is investigated experimentally. The harmonic generation process is seen to be almost completely suppressed for circular polarization opening up the possibility of producing isolated attosecond pulses via polarization gating. Particle-in-cell simulations suggest that current laser pulses are capable of generating isolated attosecond pulses with high pulse energies.

Drawing lines at the sand: evidence for functional vs. visual reef boundaries in temperate Marine Protected Areas.

Marine Protected Areas (MPAs) can either protect all seabed habitats within them or discrete features. If discrete features within the MPA are to be protected humans have to know where the boundaries are. In Lyme Bay, SW England a MPA excluded towed demersal fishing gear from 206 km(2) to protect rocky reef habitats and the associated species. The site comprised a mosaic of sedimentary and reef habitats and so 'non reef' habitat also benefited from the MPA. Following 3 years protection, video data showed that sessile Reef Associated Species (RAS) had colonised sedimentary habitat indicating that 'reef' was present. This suggested that the functional extent of the reef was potentially greater than its visual boundary. Feature based MPA management may not adequately protect targeted features, whereas site based management allows for shifting baselines and will be more effective at delivering ecosystem goods and services.

Beaming of high-order harmonics generated from laser-plasma interactions.

Beam divergences of high-order extreme ultraviolet harmonics from intense laser interactions with steep plasma density gradients are studied through experiment and Fourier analysis of the harmonic spatial phase. We show that while emission due to the relativistically oscillating mirror mechanism can be explained by ponderomotive surface denting, in agreement with previous results, the divergence of the emission due to the coherent wake emission mechanism requires a combination of the dent phase and an intrinsic emission phase. The temporal dependence of the divergences for both mechanisms is highlighted while it is also shown that the coherent wake emission divergence can be small in circumstances where the phase terms compensate each other.

Addressing the challenge of neonatal mortality.

Reducing neonatal mortality remains a challenge with an estimated 3.0 million neonatal deaths in 2011, three-quarters of these in sub-Saharan Africa and Southern Asia. The leading causes of neonatal death globally are complications of preterm birth, intrapartum-related causes and infections. While post-neonatal, under-5 deaths fell by 47% between 1990 and 2011, neonatal deaths only fell by 32% and they now account for 43% of all under-5 child deaths. This article reviews the progress in reducing neonatal deaths in high-burden countries and presents an overview of known effective interventions to reduce neonatal mortality and the challenges faced in implementing these in high-burden settings. Effective action is possible to reduce neonatal mortality, but innovative approaches to implementation will be required if these preventable deaths are to be avoided.

Methods for dealing with time-dependent confounding.

Longitudinal studies, where data are repeatedly collected on subjects over a period, are common in medical research. When estimating the effect of a time-varying treatment or exposure on an outcome of interest measured at a later time, standard methods fail to give consistent estimators in the presence of time-varying confounders if those confounders are themselves affected by the treatment. Robins and colleagues have proposed several alternative methods that, provided certain assumptions hold, avoid the problems associated with standard approaches. They include the g-computation formula, inverse probability weighted estimation of marginal structural models and g-estimation of structural nested models. In this tutorial, we give a description of each of these methods, exploring the links and differences between them and the reasons for choosing one over the others in different settings.

Nonlinear dust-acoustic solitary waves in strongly coupled dusty plasmas.

Dust-acoustic waves are investigated in a three-component plasma consisting of strongly coupled dust particles and Maxwellian electrons and ions. A fluid model approach is used, with the effects of strong coupling being accounted for by an effective electrostatic "pressure" which is a function of the dust number density and the electrostatic potential. Both linear and weakly nonlinear cases are considered by derivation and analysis of the linear dispersion relation and the Korteweg-de Vries equation, respectively. In contrast to previous studies using this model, this paper presents the results arising from an expansion of the dynamical form of the electrostatic pressure, accounting for the variations in its value in the vicinity of the wave.

A prospective study on neonatal mortality and its predictors in a rural area in Burkina Faso: can MDG-4 be met by 2015?

OBJECTIVE: To measure the neonatal mortality rate (NMR) and investigate its predictors in a rural area of Burkina Faso. STUDY DESIGN: A cohort of infants born in 24 villages in Banfora region was followed until the children were 6 months old. We estimated the risk of neonatal death and used logistic regression to identify its predictors. RESULT: Among 864 live births followed to day 28, there were 40 neonatal deaths, a NMR of 46.3 per 1000 live births (95% confidence intervals (CI): 22 to 70). Multivariable regression identified twin birth (OR=11.5, 95% CI: 4.5 to 29.8), having a nulliparous mother (odds ratio (OR)=4.3, 95% CI: 1.5 to 12.1), and birth into a polygynous household (OR=2.1, 95% CI: 1.0 to 4.7) as main predictors of neonatal death. CONCLUSION: The burden of neonatal mortality in rural Burkina Faso is very high and the observed NMRs in a predominantly rural country suggest that it is unlikely Burkina will meet fourth Millennium Development Goal (MDG-4) by 2015.

Alternatives to randomisation in the evaluation of public health interventions: design challenges and solutions.

BACKGROUND: There has been a recent increase in interest in alternatives to randomisation in the evaluation of public health interventions. We aim to describe specific scenarios in which randomised trials may not be possible and describe, exemplify and assess alternative strategies. METHODS: Non-systematic exploratory review. RESULTS: In many scenarios barriers are surmountable so that randomised trials (including stepped-wedge and crossover trials) are possible. It is possible to rank alternative designs but context will also determine which choices are preferable. Evidence from non-randomised designs is more convincing when confounders are well-understood, measured and controlled; there is evidence for causal pathways linking intervention and outcomes and/or against other pathways explaining outcomes; and effect sizes are large. CONCLUSION: Non-randomised trials might provide adequate evidence to inform decisions when interventions are demonstrably feasible and acceptable, and where evidence suggests there is little potential for harm, but caution that such designs may not provide adequate evidence when intervention feasibility or acceptability is doubtful, and where existing evidence suggests benefits may be marginal and/or harms possible.

Alternatives to randomisation in the evaluation of public-health interventions: statistical analysis and causal inference.

BACKGROUND: In non-randomised evaluations of public-health interventions, statistical methods to control confounding will usually be required. We review approaches to the control of confounding and discuss issues in drawing causal inference from these studies. METHODS: Non-systematic review of literature and mathematical data-simulation. RESULTS: Standard stratification and regression techniques will often be appropriate, but propensity scores may be useful where many confounders need to be controlled, and data are limited. All these techniques require that key putative confounders are measured accurately. Instrumental variables offer, in theory, a solution to the problem of unknown or unmeasured confounders, but identifying an instrument which meets the required conditions will often be challenging. Obtaining measurements of the outcome variable in both intervention and control groups before the intervention is introduced allows balance to be assessed, and these data may be used to help control confounding. However, imbalance in outcome measures at baseline poses challenges for the analysis and interpretation of the evaluation, highlighting the value of adopting a design strategy that maximises the likelihood of achieving balance. Finally, when it is not possible to have any concurrent control group, making multiple measures of outcome pre- and postintervention can enable the estimation of intervention effects with appropriate statistical models. CONCLUSION: For non-randomised designs, careful statistical analysis can help reduce bias by confounding in estimating intervention effects. However, investigators must report their methods thoroughly and be conscious and critical of the assumptions they must make whenever they adopt these designs.