Acropolis Educational Resources Repository
Not a member yet
31278 research outputs found
Sort by
Convergence of the deep BSDE method for FBSDEs with non-Lipschitz coefficients
No full textThis paper is dedicated to solving high-dimensional coupled FBSDEs with non-Lipschitz diffusion coefficients numerically. Under mild conditions, we provided a posterior estimate of the numerical solution that holds for any time duration. This posterior estimate validates the convergence of the recently proposed Deep BSDE method. In addition, we developed a numerical scheme based on the Deep BSDE method and presented numerical examples in financial markets to demonstrate the high performance
Canonical orbits for rapidly deforming planar microswimmers in shear flow
No full textClassically, the rotation of ellipsoids in shear Stokes flow is captured by Jeffery’s orbits. Here, we
demonstrate that Jeffery’s orbits also describe high-frequency shape-deforming swimmers moving
in the plane of a shear flow, employing only basic properties of Stokes flow and a multiple-scales
asymptotic analysis. In doing so, we support the use of these simple models for capturing shapechanging swimmer dynamics in studies of active matter and highlight the ubiquity of ellipsoid-like
dynamics in complex systems. This result is robust to weakly confounding effects, such as distant
boundaries, and also applies in the low-frequency limit
Spatially targeted digital chest radiography to reduce tuberculosis in high-burden settings: a study of adaptive decision making
No full textBackground
Spatially-targeted approaches to screen for tuberculosis (TB) could accelerate TB control in high-burden populations. We aimed to estimate gains in case-finding yield under an adaptive decision-making approach for spatially-targeted, mobile digital chest radiography (dCXR)-based screening in communities with varying levels of TB prevalence.
Methods
We used a Monte-Carlo simulation model to simulate a spatially-targeted screening intervention in 24 communities with TB prevalence estimates derived from a large community-randomized trial. We implemented a Thompson sampling algorithm to allocate screening units based on Bayesian probabilities of local TB prevalence that are continuously updated during weekly screening rounds. Four mobile units for dCXR-based screening and subsequent Xpert Ultra-based testing were allocated among the communities during a 52-week period. We estimated the yield of bacteriologically-confirmed TB per 1000 screenings comparing scenarios of spatially-targeted and untargeted resource allocation.
Results
We estimated that under the untargeted scenario, an expected 666 (95% uncertainty interval 522–825) TB cases would be detected over one year, equivalent to 8.9 (7.5–10.3) per 1000 individuals screened. Allocating the screening units to the communities with the highest (prior-year) cases notification rates resulted in an expected 760 (617−926) TB cases detected, 10.1 (8.6–11.8) per 1000 screened. Adaptive, spatially-targeted screening resulted in an expected 1241 (995–1502) TB cases detected, 16.5 (14.5–18.7) per 1000 screened. Numbers of dCXR-based screenings needed to detect one additional TB case declined during the first 12–14 weeks as a result of Bayesian learning.
Conclusion
We introduce a spatially-targeted screening strategy that could reduce the number of screenings necessary to detect additional TB in high-burden settings and thus improve the efficiency of screening interventions. Empirical trials are needed to determine whether this approach could be successfully implemented
Indirect effects of the covid-19 pandemic on childhood infection in England: population based observational study
No full textObjective To assess the impact of the covid-19 pandemic on hospital admission rates and mortality outcomes for childhood respiratory infections, severe invasive infections, and vaccine preventable disease in England.
Design Population based observational study of 19 common childhood respiratory, severe invasive, and vaccine preventable infections, comparing hospital admission rates and mortality outcomes before and after the onset of the pandemic in England.
Setting Hospital admission data from every NHS hospital in England from 1 March 2017 to 30 June 2021 with record linkage to national mortality data.
Population Children aged 0-14 years admitted to an NHS hospital with a selected childhood infection from 1 March 2017 to 30 June 2021.
Main outcome measures For each infection, numbers of hospital admissions every month from 1 March 2017 to 30 June 2021, percentage changes in the number of hospital admissions before and after 1 March 2020, and adjusted odds ratios to compare 60 day case fatality outcomes before and after 1 March 2020.
Results After 1 March 2020, substantial and sustained reductions in hospital admissions were found for all but one of the 19 infective conditions studied. Among the respiratory infections, the greatest percentage reductions were for influenza (mean annual number admitted between 1 March 2017 and 29 February 2020 was 5379 and number of children admitted from 1 March 2020 to 28 February 2021 was 304, 94% reduction, 95% confidence interval 89% to 97%), and bronchiolitis (from 51 655 to 9423, 82% reduction, 95% confidence interval 79% to 84%). Among the severe invasive infections, the greatest reduction was for meningitis (50% reduction, 47% to 52%). For the vaccine preventable infections, reductions ranged from 53% (32% to 68%) for mumps to 90% (80% to 95%) for measles. Reductions were seen across all demographic subgroups and in children with underlying comorbidities. Corresponding decreases were also found for the absolute numbers of 60 day case fatalities, although the proportion of children admitted for pneumonia who died within 60 days increased (age-sex adjusted odds ratio 1.71, 95% confidence interval 1.43 to 2.05). More recent data indicate that some respiratory infections increased to higher levels than usual after May 2021.
Conclusions During the covid-19 pandemic, a range of behavioural changes (adoption of non-pharmacological interventions) and societal strategies (school closures, lockdowns, and restricted travel) were used to reduce transmission of SARS-CoV-2, which also reduced admissions for common and severe childhood infections. Continued monitoring of these infections is required as social restrictions evolve
With or without him? Experimental evidence on gender-sensitive cash grants and trainings in Tunisia
No full textIs it possible to stimulate women’s employment by relaxing their financial and human capital constraints? Does involving husbands help or hinder the effort? To examine these questions, we randomly allocated cash grants and financial training to 1,000 poor women in Tunisia. To encourage gender dialogue, a random subset of women could invite their male partner to the training. The cash grants and financial training positively impacted women’s income generating activities, but only for women who had to attend the training alone, suggesting that gender dialogue backfired. The program also reinforced traditional gender roles: it stimulated employment of other household members as well as investments in small-scale agriculture and livestock farming—two activities traditionally undertaken by women at home. Impacts on household living standards are overwhelmingly positive
Investigating metal solidification with X-ray imaging
No full textIn the last two decades, X-ray imaging techniques have been used increasingly to study metal solidification in real-time as, thanks to advances in X-ray sources (synchrotron and laboratory-based) and detector technology, images can now be obtained with spatio-temporal resolutions sufficient to record key phenomena and extract quantitative information, primarily relating to crystal growth. This paper presents an overview of the research conducted at the University of Oxford over the last 6 years as a partner in the UK’s Future Liquid Metal Engineering (LiME) Manufacturing Hub. The focus is on in situ X-ray radiography to investigate the solidification of Al alloys, including the formation of primary α-Al crystals, and the formation and growth of secondary intermetallic phases. Technologically, the thrust is to understand how to control as-cast phases, structures and element distributions, particularly elements associated with recycling, as a means to facilitate greater recirculation of aluminium alloys. We first present studies on refinement of primary α-Al, including extrinsic grain refinement using inoculation and intrinsic refinement based on dendrite fragmentation. Second, we describe studies on intermetallic phase formation and growth, because intermetallic fraction, morphology and distribution are frequently a limiting factor of alloy mechanical properties and recyclability. Then we present some of the latest progress in studying liquid flow during solidification and associated hot tear formation. Finally, future research directions are described
Sleep in the time of COVID-19: findings from 18000 school-aged children and adolescents in the UK during the first national lockdown
No full textStudy Objectives
Sleep is essential to young people’s wellbeing, yet may be constricted by the adolescent delayed sleep phase coupled with school start times. COVID-19 restrictions caused major disruptions to everyday routines, including partial school closures. We set out to understand changes in students’ self-reported sleep quality, and associations with mental wellbeing and interpersonal functioning, during these restrictions.
Methods
The OxWell school survey—a cross-sectional online survey—collected data from 18 642 children and adolescents (aged 8–19 years, 60% female, school year 4–13) from 230 schools in southern England, in June–July 2020. Participants completed self-report measures of the impact of COVID-19 restrictions on sleep quality, happiness, and social relationships. Sleep timing was compared with data collected from 4222 young people in 2019.
Results
Females and older adolescents were more likely to report deteriorations in sleep during the national lockdown. Regression analysis revealed that changes in happiness (β = .34) and how well students were getting on with others in their household (β = .07) predicted change in sleep quality. Students’ bedtimes and wake times were later, and sleep duration was longer in 2020 compared to the 2019 survey. Secondary school students reported the greatest differences, especially later wake times.
Conclusions
During COVID-19 restrictions, sleep patterns consistent with adolescent delayed sleep phase were observed, with longer sleep times for secondary school students in particular. Perceived deteriorations in sleep quality were associated with reductions in happiness and interpersonal functioning, highlighting the importance of including sleep measures in adolescent wellbeing research
Τα Μνημεία της Ακρόπολης μέσα στο Μουσείο Ακρόπολης
Full text linkΣχέδιο προετοιμασίας ανεξάρτητης επίσκεψης στο Μουσείο Ακρόπολης με θέμα: "Τα Μνημεία της Ακρόπολης μέσα στο Μουσείο Ακρόπολης
Fluid Mechanics: the quintessential complex system
No full textThe 2021 Nobel Prize in Physics recognizes advances in the understanding of complex systems, and underscores that ‘complex’ does not mean ‘imponderable’