Field-dependent abundances of hydride molecular ions in atom probe tomography of III-N semiconductors.

We investigate the microscopic behaviour of hydrogen-containing species formed on the surface of III-N semiconductor samples by the residual hydrogen in the analysis chamber in laser-assisted atom probe tomography (APT). We analysed AlGaN/GaN heterostructures containing alternate layers with a thickness of about 20 nm. The formation of H-containing species occurs at field strengths between 22 and 26 V/nm and is independent of the analysed samples. The 3D APT reconstruction makes it possible to map the evolution of the surface behaviour of these species issued by chemical reactions. The results highlight the strong dependence of the relative abundances of hydrides on the surface field during evaporation. The relative abundances of the hydrides decrease when the surface field increases due to the evolution of the tip shape or the different evaporation behaviour of the different layers.

Enhancing the value of death registration with verbal autopsy data: a pilot study in the Senegalese urban population in 2019.

BACKGROUND: There is no source of data on causes of death in Senegal that covers both community and hospital deaths. Yet the death registration system in the Dakar region is relatively complete (>80%) and could be expanded to provide information on the diseases and injuries that led to death. METHODS: In this pilot study, we recorded all deaths that occurred over 2 months and were reported in the 72 civil registration offices in the Dakar region. We selected the deaths of residents of the region and administered a verbal autopsy to a relative of the deceased to identify the underlying causes of death. Causes of death were assigned using the InterVA5 model. RESULTS: The age structure of deaths registered at the civil registry differed from that of the census, with a proportion of infant deaths about twice as high as in the census. The main causes of death were prematurity and obstetric asphyxia in newborns. Meningitis and encephalitis, severe malnutrition, and acute respiratory infections were the leading causes from 1 month to 15 years of age. Cardiovascular diseases accounted for 27% of deaths in adults aged 15-64 and 45% of deaths among adults above age 65, while neoplasms accounted for 20% and 12% of deaths in these two age groups, respectively. CONCLUSIONS: This study demonstrates that the epidemiological transition is at an advanced stage in urban areas of Dakar, and underlines the importance of conducting regular studies based on verbal autopsies of deaths reported in civil registration offices.

Vaccination card availability and childhood immunization in Senegal.

BACKGROUND: The World Health Organization recommends recording vaccination status according to maternal recall in countries where administrative reporting systems are insufficiently reliable, as maternal recall in developing countries has been shown to be quite reliable compared with data from vaccination cards. This study aimed to investigate childhood vaccination coverage and its determinants according to the mothers' presentation of vaccination cards. METHODS: The data come from the 2017 Senegalese Demographic and Health Survey, a nationally representative household survey of women aged 15-49 years, with a questionnaire focusing on children's health. This analysis was restricted to children aged 12-35 months (n = 4032) and it assessed vaccination coverage and associated sociodemographic factors with weighted multivariate logistic regressions. Stratified multivariate logistic regressions were also performed to investigate factors associated with routine childhood immunization uptake of the Bacillus Calmette-Guérin (BCG) vaccine, recommended for administration shortly after birth, as well as of the vaccines against yellow fever and measles (recommended at 9 months). RESULTS: Comparison of vaccination coverage estimates according to the vaccination card or parental recall resulted in a 5-10% difference in estimated coverage for the BCG, pentavalent, measles, and yellow fever vaccines, but a huge difference for the polio vaccine (93.0% with the card, 32.0% without it). Presentation of the vaccination card was correlated with mothers' attendance at health facilities (suggesting it serves as a concrete manifestation of a bond between mothers and the healthcare system) and their region of residence, but it was not correlated with usually strong predictors of childhood vaccination, such as maternal education level. Factors associated with vaccinations differed depending on whether they were administered shortly after birth or later on. CONCLUSIONS: Maternal recall was found to be quite reliable except for oral polio vaccination, which raises the possibility that complete immunization coverage rates could have been significantly underestimated due to potential confusion between injection and vaccination. Considering the ability to present vaccination cards as the materialization of a bond with the healthcare system, the decision path leading to vaccination among those who lack such a bond appears longer and more likely to be driven by supply-side effects.

Determinants of childhood immunizations in Senegal: Adding previous shots to sociodemographic background.

Introduction. Today, in Sub-Saharan Africa, vaccine-preventable diseases still contribute heavily to high child mortality. Maintaining high coverage rates for childhood vaccines and reducing related social inequalities are public health priorities in Senegal. Our aim was to investigate the determinants of childhood vaccination, including sociodemographic factors and previous vaccine-related decision-making.Methods. Data come from the 2016 Senegalese Demographic and Health Survey, a nationally representative household survey targeting women aged 15-49, with a questionnaire focusing on health and reproductive issues, including their children's health. We restricted the analysis to children aged 12-23 months (n = 1,143). We used bivariate and multivariate analyses for investigating the determinants of several childhood vaccinations (Bacillus Calmette-Guérin, pentavalent, polio, measles and yellow fever vaccines), including sociodemographic factors and previous shots.Results. We identified two main sociodemographic predictors of childhood vaccination in Senegal: the mother's education level, which was strongly and positively correlated to every vaccination considered, except from the BCG vaccination, and the region of residence, with higher vaccination coverage rates in the Centre and West of Senegal. Moreover, previous shots were also strongly predictive of subsequent shots.Conclusion. The positive impact of mother's education on child vaccination illustrates the wide-ranging benefits of educating girls, while the regional variability of immunization rates requires more research to be better understood. Previous shots are probably a proxy variable for unobservable factors strongly correlated to vaccinations, but beyond this 'proxy effect', they may also have their own specific effect on following shots. We believe this topic deserves further research.

Decision making environment on Rift Valley fever in Ferlo (Senegal).

The Rift Valley fever (RVF), which first appeared in Kenya in 1912, is an anthropozoonosis widespread in tropical areas. In Senegal, it is particularly felt in the Ferlo area where a strong presence of ponds shared by humans, cattle and vectors is noted. As part of the studies carried out on the environmental factors which favour its start and propagation, the focus of this paper is put on the decision making process to evaluate the impacts, the interactions and to make RVF monitoring easier. The present paper proposes a model based on data mining techniques and dedicated to trade experts. This model integrates all the involved data and the results of the analyses made on the characteristics of the surrounding ponds. This approach presents some advantage in revealing the relationship between environmental factors and RVF transmission vectors for space-time epidemiology monitoring purpose.