Mathematical analysis of the dynamics of COVID-19 in Africa under the influence of asymptomatic cases and re-infection

Coronavirus pandemic (COVID-19) hit the world in December 2019, and only less than 5% of the 15 million cases were recorded in Africa. A major call for concern was the significant rise from 2% in May 2020 to 4.67% by the end of July 15, 2020. This drastic increase calls for quick intervention in the transmission and control strategy of COVID-19 in Africa. A mathematical model to theoretically investigate the consequence of ignoring asymptomatic cases on COVID-19 spread in Africa is proposed in this study. A qualitative analysis of the model is carried out with and without re-infection, and the reproduction number is obtained under re-infection. The results indicate that increasing case detection to detect asymptomatically infected individuals will be very effective in containing and reducing the burden of COVID-19 in Africa. In addition, the fact that it has not been confirmed whether a recovered individual can be re-infected or not, then enforcing a living condition where recovered individuals are not allowed to mix with the susceptible or exposed individuals will help in containing the spread of COVID-19.     

Remediation of <Superscript>137</Superscript>Cs radionuclide in nuclear waste effluents by polymer composite: adsorption kinetics,isotherms and gamma irradiation studies

Polypyrrole is incorporated with activated carbon in large size dopant solution and investigated for ¹³⁷Cs removal studies. Adsorption experiments showed optimum conditions within 240 min contact time, pH 6, 0.2 g adsorbent and?≤?100 mg/l adsorbate dose, respectively, while the kinetic data followed pseudo-first-order model. Isotherm data were reproducible by the Langmuir isotherm yielding 23 mg/g maximum sorption capacity. Regeneration of adsorbent was attempted and indicated promising results within three cycles. The surface behavior has also been examined and revealed a well-ordered structure under gamma irradiation. This is a cheap adsorbent to consider and has also proven to possess higher sorption capacity than most highly-cost inorganic materials in use.     

A first‐principles study of diatomic NiAl: Ground state,structure, and spectroscopic constants

A computational study of diatomic NiAl is reported. Molecular properties evaluated include the equilibrium bond length (r_e), equilibrium stretching frequency (ω_e), doublet‐quartet energy splitting, and nickel‐aluminum bond strength. Several interesting conclusions have resulted from this research. First, convergence in calculated properties is smoother with recently reported correlation consistent basis sets than earlier basis sets for Ni and Al. Second, with the exception of bond strength, basis set limit properties extrapolated using correlation basis sets are in agreement with reported data. Third, this research suggests that caution may be needed with regard to the use of DFT for developing interatomic potentials for larger scale simulations. For example, B97‐1 showed better agreement with reported r_e for ²NiAl than B3LYP. However, the situation was reversed for the calculation of ω_e. With respect to bond strength, the situation is unclear due to the scatter among experiment and calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Oxidation of thiourea and thioacetamide by octacyanomolybdate(v) anion in perchloric acid

Summary The kinetics of the reduction of octacyanomolybdate(V) anion by thiourea and thioacetamide have been studied in aqueous HClO₄ at constant ionic strengthI=0.10 mol dm^–3 (NaClO₄). The rate of oxidation of these substrates by the oxidant shows a first order dependence in both the oxidant and the substrates and while the thiourea system exhibits an inverse first-order dependence on [H⁺] that of thioacetamide is found to be first-order in [H⁺]. The variation observed in [H⁺] dependences in these reactions is attributed to the nature of the thiourea in the pH range used in this study and the inductive effect of the methyl group in thioacetamide. A mechanistic interpretation of these observations is advanced.     

Synergy effect of boron and cobalt in B2O3-SBA-15-(Co)Mo catalyst for efficient hydrodesulfurization of liquid fuels

Research on Chemical Intermediates - The contributory effect of surface acidity is significant to desulfurize heavy recalcitrant organosulfur compounds effectively. This research explores the...     

Opportunities and challenges of thin-film boron-doped diamond electrochemistry for valuable resources recovery from waste: Organic,inorganic, and volatile product electrosynthesis

Thin-film boron-doped diamond (BDD) electrochemistry has made a tremendous progress in electrochemical synthesis/recovery of high-added value products from aqueous and gaseous waste streams. The distinguished electrochemical characteristic of this electrode has made this material emerging and successfully used in electrosynthetic transformations, besides its destructive and powerful performance in disinfection and detoxification of wastewaters. Organic electrosynthesis is achieved by the oxyl radical oxidation formed at BDD, peroxo compounds electrosynthesis is attained by oxidation of corresponding anions at the BDD surface, whereas electrochemical conversion of SO₂, CO₂, NO₃^?, and NH₃ to value-added products occurs by BDD cathodic reduction process. There are still some challenges needed to address for seamless scale-up and translation into application of this future technology.     

The kinetics of the oxidation of iodide and thiocyanate ions by 12-tungstocobaltate(III)

The rates and mechanism of the reaction of 12-tungstocobaltate(III) anion with thiocyanate and iodide ions have been examined in aqueous acidic solution and constant ionic strength I = 1.00M (LiClO₄). The reactions follow second-order kinetics, i.e. first-order in both the oxidant and the reductant and the rate constants are found to be independent of hydrogen ions in the range [H⁺] = 0.10–1.00M. Outer-sphere mechanism is postulated for the systems based on the relative inertness of the oxidant and linear free energy relations are employed in demonstrating that in the reaction involving thiocyanate ion, the rate determining step is the diffusion apart of the product while the corresponding step in the iodide reaction is the electron transfer. The latter reaction is also catalysed by both bromide and chloride ions and this is rationalised in terms of possible stabilization of atomic iodine as product by these halide ions.     

Stoichiometry and kinetics of the oxidation of hydroxylammonium ion by 12-tungstocobaltate(III) anion in aqueous solution

Summary The stoichiometry and kinetics of the oxidation of hydroxylammonium ion by the 12-tungstocobaltate(III) anion has been studied in hydrochloric acid medium. The ratio of mols of oxidant consumed per mol of hydroxylammonium ion is 11 and the evolution of nitrogen is confirmed. In the 0.1–1.0 mol dm^–3 [H⁺] region, the oxidation is acid-independent and obeys the empirical rate law: –d[oxidant]/dt=k[oxidant] [reductant] where k=(3.51±0.18)×10^–4 mol^–1dm³s^–1 at 22.4±0.1C and I=2.0 mol dm^–3 (NaCl). Possible reaction steps and mechanism are suggested.     

Electron transfer at an encapsulated cobalt(III) centre: kinetics of oxidation of thiourea and 1,1,3,3-tetramethyl-2-thiourea in aqueous acidic media

Summary The stoichiometries, kinetics and mechanisms of oxidation of (NH₂)₂CS (1) and (Me₂N)₂CS (2) to the corresponding disulphides by Co^IIIM (M = W₁₂O₄₀ ^∞-) in aqueous HC1O₄ were investigated. The reaction with (1) follows the empirical rate law- d[oxidant] = k[reductant][oxidant] where k = 12.5 ± 0.3 m⁻¹ s⁻¹ at 25° C, while that with (2) follows the equation- d[oxidant] = a + b [reductant] [reductant] [oxidant] where a = 5.4 × 10⁴ M⁻¹s⁻¹ and b = 3.3 × 10⁶M⁻² s⁻¹ at 25° C. Free radicals are important in the reactions and possible reaction mechanisms are suggested and discussed.