4 research outputs found

    Synthesis and Characterization of Spinel Ferrite Co0.8Fe2.2O4 Nanoparticle

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    Cobalt ferrite Co0.8Fe2.2O4 nanoparticles were prepared using the sol-gel auto combustion process. The effects of calcination temperature on structural, magnetic, and electrical properties were studied. The cubic spinel phase fashioning of ferrite structure was confirmed using Fourier Transform-Infrared Spectroscopy (FT-IR) and X-ray Diffraction Patterns (XRD). The size of the formed crystallite of ferrite samples is ranged from 24.530 to 49.067 nm and it is found to be dependent on calcination. According to the images, which were taken by a Field Emission-Scanning Electron Microscope (FE-SEM), the particle size increases with raising the calcination temperature. Energy Dispersive Spectrum (EDS) was used to confirm the presence of Co, Fe, and O in all samples. A Vibrating Sample Magnetometer (VSM) was used to study the magnetic properties such as coercivity, saturation magnetization, and remanence field for the as-burnt and calcined samples. All samples exhibited ferrimagnetic behavior. As the calcination temperature rises, saturation magnetization (M_s), remanent magnetization (M_r), and squareness ratio (M_r/ M_s) increased. This behavior is related to the spin canting and disturbance in the surface spin. At room temperature, the dielectric loss factor (Δ''), dielectric loss angle (tanÎŽ), dielectric constant (Δ'), and the conductivity σ_ac of all samples were examined as a function of frequency using the LCR meter. The changes in dielectric properties have been characterized at frequencies ranged from 50Hz to 2MHz based on Koop's theory, Maxwell-Wagner polarization, and electron hopping. As frequency rose, all-dielectric properties exhibited natural behavior

    The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

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    INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
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