Calcium carbonate particle formation through precipitation in a stagnant bubble and a bubble column reactor

The precipitation of CaCO3 via CO2 bubbling using well-defined membranes was used in this study to produce particles of a variety of structures. Studies into the mechanisms of particle formation via this method are limited and are mainly specific to hollow structures. Using a range of analytical techniques, particles produced with a stagnant bubble and in bubbling systems (crossflow and vertical flow) were investigated. The stagnant bubble work concluded that the particles are produced both in bulk but also at the gas/liquid interface which then fall down and collect at the base of the bubble, whereas in a dynamic system the bubble wake has an important role in precipitation of such particles. Precipitation occurs as the solution pH drops due to CO2 bubbling (acidic gas) and these particles are initially comprised of a solid core. As the pH drops bubbling (acidic gas) and these particles are initially comprised of a solid core. As the pH drops further, these particles transform to ones with hollow core and the pH plays an important role in controlling the particle shell thickness. Allowing the particles to age in solution allows for transformation of such particles from vaterite to calcite. Finally, the particle structure can also be altered by changing the bubbling set up as having a recirculation loop leads to the formation of particles exhibiting a stacked cube

Measurements of Submicron Particle Adsorption and Particle Film Elasticity at Oil-Water Interfaces

The influence of particle adsorption on liquid/liquid interfacial tension is not well understood, and much previous research has suggested conflicting behaviors. In this paper we investigate the surface activity and adsorption kinetics of charge stabilized and pH-responsive polymer stabilized colloids at oil/water interfaces using two tensiometry techniques: (i) pendant drop and (ii) microtensiometer. We found, using both techniques, that charge stabilized particles had little or no influence on the (dynamic) interfacial tension, although dense silica particles affected the "apparent" measured tension in the pendent drop, due to gravity driven elongation of the droplet profile. Nevertheless, this apparent change additionally allowed the study of adsorption kinetics, which was related qualitatively between particle systems by estimated diffusion coefficients. Significant and real interfacial tension responses were measured using ∼53 nm core-shell latex particles with a pH-responsive polymer stabilizer of poly(methyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (pMMA-b-pDMAEMA) diblock copolymer. At pH 2, where the polymer is strongly charged, behavior was similar to that of the bare charge-stabilized particles, showing little change in the interfacial tension. At pH 10, where the polymer is discharged and poorly soluble in water, a significant decrease in the measured interfacial tension commensurate with strong adsorption at the oil-water interface was seen, which was similar in magnitude to the surface activity of the free polymer. These results were both confirmed through droplet profile and microtensiometry experiments. Dilational elasticity measurements were also performed by oscillation of the droplet; again, changes in interfacial tension with droplet oscillation were only seen with the responsive particles at pH 10. Frequency sweeps were performed to ascertain the dilational elasticity modulus, with measured values being significantly higher than previously reported for nanoparticle and surfactant systems, and similar in magnitude to protein stabilized droplets.</p

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

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

Latex Parameters Results - Manufacture of Poly (methyl methacrylate) Microspheres using Membrane Emulsification

Latex Parameters Results - Table.A cross - flow membrane emulsification [XME] technique was used here in the preparation of poly (methylmethacrylate) [PMMA] microspheres at a 1&ndash;10 L / h scale, to demonstrate its application for such a manufacturing challenge.&nbsp; We demonstrate here that for an appropriate formulation, equivalent control can be gained for a pre-cursor emulsion in a batch suspension polymerisation process

Production of solid-stabilised emulsions through rotational membrane emulsification: influence of particle adsorption kinetics

There is currently a significant interest in the production of stable emulsions using particulate emulsifiers. A key design and manufacturing challenge in such systems is the production of emulsions with controlled droplet sizes and narrow polydispersity; one candidate production technique is membrane emulsification. In this study we demonstrate that under optimal conditions, highly stable near monodisperse tricaprylin droplets stabilised with 800 nm silica colloids can be achieved using Rotating Membrane Emulsification (RME). We report the influence of various mechanical and chemical parameters on the droplet sizes and size distributions. The optimal conditions for highly stable emulsions with narrow size distributions using the RME approach are described. Investigating the rotational speed and particle concentration in particular highlights the importance of particle adsorption kinetics onto a growing droplet on the detachment of that droplet from the membrane. The data clearly show that if the particles attach and adsorb to the interface before a critical droplet detachment time, stable monodisperse droplets are produced. However, if the adsorption time takes longer than this critical value, the partially stabilized droplets can coalesce and we observe a wider size distribution

Data_Sheet_1_Influence of pH-Responsive Monomer Content on the Behavior of Di-Block Copolymers in Solution and as Stabilizers of Pickering Latex Particle Emulsifiers.docx

<p>In this study, diblock copolymers poly(methyl methacrylate)—block—poly (2-dimethylaminoethyl methacrylate) (pMMA-b-pDMAEMA) are investigated for the steric stabilization of latex particles and the subsequent use of these latex particles as Pickering emulsifiers. Solution properties of the diblock copolymers highlight that the pDMAEMA block length influences the critical micelle concentration (CMC) and micelle hydrodynamic diameter in response to changes in pH and the pK_a. The block length can also be used as a way to control the particle size of sterically stabilized polystyrene latex particles prepared via emulsion polymerization. The suspension properties of these latex particles are also presented. Emulsion studies using these latex particles as emulsifiers show that both continuous phase pH and electrolyte concentration affect emulsion stability to coalescence. At high pH, stable emulsions are formed due to the affinity of the particles to the interface. At low pH, protonation of the amine groups reduces the affinity and thus droplet coalescence is observed. Increasing the electrolyte concentration improves emulsion stability, but causes an increase in droplet size due to adsorption of flocculated/aggregated particles. Finally, it is shown that these latex particles can be used in conjunction with membrane emulsification techniques to produce emulsions with low polydispersity.</p

Behavior of pH-Sensitive Core Shell Particles at the Air–water Interface

In this article, the adsorption of latex core-responsive polymer–shell nanoparticles at the air–water interface is investigated using a Langmuir trough. Phase transition isotherms are used to explore their responsive behavior at the interface as a function of changes in the pH of the subphase. By adjusting the pH of the water prior to particle deposition, we probe the effect of the stabilizing polymer wetting by the water subphase on the stability of these particles at the air–water interface. In addition, by initially compressing a stable film of adsorbed particles and then subsequently changing the pH of the subphase we study desorption of these particles into the water phase

Assessment of Micronutrient Situation among Reproductive-Age Women (15–49) and Under-Five Children in Sudan

Background: Micronutrient malnutrition is a form of undernutrition that causes diseases, and this is mainly due to insufficient intake of nutrients in daily foods. The status of micronutrients for people in Sudan remains scarce, and information is limited. The aim of this study is to highlight the status of micronutrients among women of reproductive age (15–49 years of age) and their children in Sudan. Methods: This manuscript is a quantitative descriptive study, based on the data from Sudan Micronutrient Survey (SMS); it is part of the second round of the Simple Spatial Survey Method (S3M II) in Sudan (a total of 93,882 households). Results: The level of consumption of vitamin A-rich foods was found to be moderate at 67.36% for reproductive-age women and low at 23.44% for under-five children. Similarly, consumption rate of vitamin B-rich foods among reproductive-age women was 62.13%, and low for children at 11.02%. The consumption of iron-, calcium-, and zinc-rich foods was moderate among women (66.75%, 47.69%, 69.72%, respectively) and very low in children (12.28%, 17.62%, 14.99%, respectively). The iron deficiency prevalence was 47% in non-pregnant women, 58% in pregnant women, and 54% in children. The prevalence of anemia was 30% in non-pregnant women, 37% in pregnant women, and 48% in children. Generally, urinary iodine concentration was inadequate in lactating and non-pregnant women as well as in pregnant women. Most indicators of micronutrients in Sudan for children and women of reproductive age were highly significant. Sudan needs more efforts to create an enabling environment through legislation, policies, and strategies to strengthen the nutrition-sensitive and specific interventions and improving status of micronutrients among women and children, focusing on food fortification, food supplements, and counseling on micronutrients intake for mothers during antenatal and postnatal services as well as raising community awareness