Covid-19: Perspectives Across Africa

This book emanated from the Society for the Advancement of Science in Africa's (SASA) Seventh Annual International (digital) Conference: Joint SASA and Ugandan Ministry of Health October 15, 2020 – January 14, 2021, Kampala, Uganda. The chapters in this book were solicited from presenters and also from other authors familiar with the impact of Covid-19 in Africa. There are 21 chapters, all together offering a range of perspectives from a variety of angles.SASA (Society for the Advancement of Science in Africa

The Peak of the Fallback Rate from Tidal Disruption Events: Dependence on Stellar Type

A star completely destroyed in a tidal disruption event (TDE) ignites a luminous flare that is powered by the fallback of tidally stripped debris to a supermassive black hole (SMBH) of mass $M_{\bullet}$. We analyze two estimates for the peak fallback rate in a TDE, one being the "frozen-in" model, which predicts a strong dependence of the time to peak fallback rate, $t_{\rm peak}$, on both stellar mass and age, with $15\textrm{ days} \lesssim t_{\rm peak} \lesssim 10$ yr for main sequence stars with masses $0.2\le M_{\star}/M_{\odot} \le 5$ and $M_{\bullet} = 10^6M_{\odot}$. The second estimate, which postulates that the star is completely destroyed when tides dominate the maximum stellar self-gravity, predicts that $t_{\rm peak}$ is very weakly dependent on stellar type, with $t_{\rm peak} = \left(23.2\pm4.0\textrm{ days}\right)\left(M_{\bullet}/10^6M_{\odot}\right)^{1/2}$ for $0.2\le M_{\star}/M_{\odot} \le 5$, while $t_{\rm peak} = \left(29.8\pm3.6\textrm{ days}\right)\left(M_{\bullet}/10^6M_{\odot}\right)^{1/2}$ for a Kroupa initial mass function truncated at $1.5 M_{\odot}$. This second estimate also agrees closely with hydrodynamical simulations, while the frozen-in model is discrepant by orders of magnitude. We conclude that (1) the time to peak luminosity in complete TDEs is almost exclusively determined by SMBH mass, and (2) massive-star TDEs power the largest accretion luminosities. Consequently, (a) decades-long extra-galactic outbursts cannot be powered by complete TDEs, including massive-star disruptions, and (b) the most highly super-Eddington TDEs are powered by the complete disruption of massive stars, which -- if responsible for producing jetted TDEs -- would explain the rarity of jetted TDEs and their preference for young and star-forming host galaxies.Comment: 10 pages, 4 figures, ApJL accepte

The Peak of the Fallback Rate from Tidal Disruption Events: Dependence on Stellar Type

A star completely destroyed in a tidal disruption event (TDE) ignites a luminous flare that is powered by the fallback of tidally stripped debris to a supermassive black hole (SMBH) of mass M•. We analyze two estimates for the peak fallback rate in a TDE, one being the “frozen-in” model, which predicts a strong dependence of the time to peak fallback rate, tpeak, on both stellar mass and age, with 15 days ≲ tpeak ≲ 10 yr for main sequence stars with masses 0.2 ≤ M⋆/M⊙ ≤ 5 and M• = 106M⊙. The second estimate, which postulates that the star is completely destroyed when tides dominate the maximum stellar self-gravity, predicts that tpeak is very weakly dependent on stellar type, with t MM peak • = (23.2 +4.0 days) (M./10 6M⊙) 1/2 for 0.2 ≤ M⋆/M⊙ ≤ 5, while tpeak = (29.8 +3.6 days) (M./10 6M⊙) 1/2 for a Kroupa initial mass function truncated at 1.5M⊙. This second estimate also agrees closely with hydrodynamical simulations, while the frozen-in model is discrepant by orders of magnitude. We conclude that (1) the time to peak luminosity in complete TDEs is almost exclusively determined by SMBH mass, and (2) massive-star TDEs power the largest accretion luminosities. Consequently, (a) decades-long extra-galactic outbursts cannot be powered by complete TDEs, including massive-star disruptions, and (b) the most highly super-Eddington TDEs are powered by the complete disruption of massive stars, which—if responsible for producing jetted TDEs—would explain the rarity of jetted TDEs and their preference for young and star-forming host galaxies

Assessment and development of remote sensing based algorithms for water quality monitoring in Olushandja Dam, North-Central Namibia.

Olushandja Dam is amongst Namibia’s inland water bodies that store and supply water to towns such as Outapi, Oshikuku and Oshakati. The dam is part of a complex water supply system that transports inter-basin water from the Kunene River Basin into Cuvelai Basin in the north-central regions of Namibia via a canal. There are potential sources of pollution along the route of the canal and around the dam which have effects on the water quality in the canal and eventually in the Olushandja Dam. Therefore, frequent and continuous monitoring of water quality is needed to allow timely decisions on the management of this critical resource. Specifically, the study sought to measure water quality at selected points in the dam and on the canal. This study used Landsat 8, 30 m resolution imagery to derive water quality parameters using retrieval algorithms. Water quality parameters included total suspended matter, turbidity, total nitrogen, nitrates, ammonia, total phosphorus and total algae counts. The study was carried out from November 2014 to June 2015. The retrieval algorithms were developed from a simple regression analysis between reflectance values of satellite images and field measurements. Statistical analyses were carried out to assess correlation between Landsat 8 predicted and field measured data. The field measurements showed that the dam and canal water is of low risk to human and is suitable for livestock watering. Turbidity levels exceeded the recommended limits set by NamWater is thus likely to cause complications in drinking water treatment as well as human and aquatic life. The study also found that all water quality parameter regression algorithms had high correlation coefficients (R2) which was between 0.980-0.999. Therefore, the study concludes that the developed regression algorithms are best fit to predict water quality parameters from satellite data. Remote sensing is therefore recommended for frequent and continuous monitoring of Olushandja Dam as it has the ability to provide information about surface water quality and Namibia has cloud free sky most times of the year. However, accurate monitoring data acquired using traditional methods remain an important input into remote sensing process for prediction of water quality.,WaterNe

Associative DNA methylation changes in children with prenatal alcohol exposure

Aim: Prenatal alcohol exposure (PAE) can cause fetal alcohol spectrum disorders (FASD). Previously, we assessed PAE in brain tissue from mouse models, however whether these changes are present in humans remains unknown. Materials & methods: In this report, we show some identical changes in DNA methylation in the buccal swabs of six children with FASD using the 450K array. Results: The changes occur in genes related to protocadherins, glutamatergic synapses, and hippo signaling. The results were found to be similar in another heterogeneous replication group of six FASD children. Conclusion: The replicated results suggest that children born with FASD have unique DNA methylation defects that can be influenced by sex and medication exposure. Ultimately, with future clinical development, assessment of DNA methylation from buccal swabs can provide a novel strategy for the diagnosis of FASD

Economic viability of splitting nitrogen fertilizer in maize (Zea mays L.): case of Lubumbashi, southeastern DR Congo

Objectives: Fertilizers mineralize throughout the growing season and the availability of nitrogen may not always coincide with the cycle of crop growth. Thus, fractionation of nitrogen and its application on two improved varieties of maize, UNILU and PAN 53, was explored in order to contribute to increased productivity of maize, the main food crop in the region of Lubumbashi. Methods and results: A trial was set up at the farm Kasapa to study the profitability of the splitting of urea, considering the dose currently popularized by the firm Omnia (for a density of 33333 plants per hectare 400Kg NPK and 800Kg urea divided into two doses: 400kg of urea at 30 days after sowing and 400kg at 75 days). Different frequencies of urea fractionation, namely 2, 3, 4, 5 and the application to the single dose were tested. The observations related on the emergence rate, number of days to flowering male and female, the male inflorescence height and insertion of ear, the lodging resistance, number of ear by foot, the average weight of grains per spike, 1000 grain weight and yield. The results of the ANOVA showed that the agronomic parameters studied were not influenced by the varieties and frequency splitting of urea. Conclusion and potential application of research: the results of the acceptability index showed that fractionation is not advising against the costs of spreading and mounding that negatively affect the profitability of growing corn. Furthermore, this study is a contribution to the profitability of fertilizer use in maize, considering the high cost of work (including spreading and mounding) is an obstacle to increased maize cultivation in middle peasant. Keywords: split, variety, urea, UNILU, Pan 53, corn J. Appl. Biosci. 201