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.     

Theory of nuclear quadrupole interactions in aluminum and copper metals in presence of muon

The electric field gradients at²⁷Al and⁶³Cu nuclei which are nearest neighbors to the muon in the face-centered cubic metals aluminum and copper, with muon at an octahedral interstitial site, are studied. The electron density fluctuations needed for the evaluation of the electronic, or valence, contributions to field gradients are taken from earlier investigations involving the spherical solid approximation. The enhancement factors a that have to be applied to the electric field-gradients obtained from these approximations, due to the departures of the electronic wave-functions from plane-wave character, and the incorporation of antishielding effects, have been obtained for both APW and OPW approaches to the conduction electron wave-functions and good agreement is found between the results by the two approaches. Size effects due to the lattice distortion associated with the presence of the muon are included through actual point ion summations using available calculated displacements of the ions surrounding the muon. The valence contributions are the dominant ones but the size effect contributions are also significant. The net field-gradient obtained for the²⁷Al site is significantly smaller than experiment while that for⁶³Cu is substantially larger than experiment. Possible sources that could lead to better agreement with experiment are discussed and it is concluded that major improvement is needed in the valence effect contributions in both metals.     

Theoretical Analysis of Viscous Coupling in Two-phase Flow through Porous Media

Theoretical analysis is presented to quantify the viscous coupling effect in two-phase flow through porous media. The analysis is based on the principle of potential difference equations as well as on the interfacial contact area and partition concept. The analysis shows that viscous coupling effect is negligible throughout the normalized saturation range. The expression, Xϕ ², was developed for the quantification of the parameter that controls the amount of viscous coupling, where X was theoretically found to have a maximum value of 2.     

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.     

Synthesis and crystal structure of bis(O-methyl hydrogenato carbonodithioate)-Pb(II): structural,optical and photocatalytic studies of PbS nanoparticles from the complex

Abstract

Lead(II) methyl xanthate [Pb(S₂COMe)₂] was synthesized and characterized by single crystal X-ray crystallography. The molecular structure showed a distorted tetrahedral geometry around Pb(II) with each monomeric unit linked with another through Pb···S interactions. The compound was used to prepare hexadecylamine capped PbS (HDA-PbS) and oleylamine capped PbS (OLA-PbS) nanoparticles. The PbS nanoparticles were indexed to the cubic PbS crystalline phase with particle sizes of 4.5 – 34.5?nm. The estimated optical bandgaps obtained from the tauc’s plots were 3.47 and 3.30?eV for HDA-PbS and OLA-PbS, respectively, which are blue shifted in comparison to bulk PbS. The photodegradation of methylene blue using PbS as photocatalyst shows that HDA-PbS have the best degradation efficiency of 77.70% after 240?min.     

Synthesis and characterization of metal complexes of N-alkyl-N-phenyl dithiocarbamates

Ammonium N-ethyl-N-phenyl dithiocarbamate (L¹) and N-butyl-N-phenyl dithiocarbamate (L²), and their group 12 metal complexes formulated as Zn₂L¹₄, CdL¹₂, HgL¹₂, Zn₂L²₄, CdL²₂, HgL²₂ have been synthesized and characterized by elemental analyses, IR, ¹H and ¹³C NMR spectroscopy. The crystal structures of the zinc complexes (Zn₂L¹₄ and Zn₂L²₄) are also reported. Single crystal analyses of the two complexes revealed the presence of distorted trigonal bipyramidal and tetrahedral coordination geometry about the metal ions. The dithiocarbamate acts as bidentate chelating and bidentate bridging ligands between the metal ions giving centrosymmetric dimeric molecules. The apparent substitution of the ethyl substituents in L¹ by the butyl groups in L² results in profound change in structure.