Adama University

About: Adama University is a education organization based out in Nazrēt, Ethiopia. It is known for research contribution in the topics: Population & Adsorption. The organization has 840 authors who have published 1010 publications receiving 5547 citations. The organization is also known as: Adama Science and Technology University & ቴክኖሎጂ ዩኒቨርሲቲ, አዳማ ሳይንስና ቴክኖሎጂ ዩኒቨርሲቲ.

Sorption behaviour of bamboo fibre reinforced composites, why do they retain their properties?

Abstract: The influence of moisture on the mechanical properties of bamboo fibre reinforced composites was assessed both for static and hygroscopic cyclic conditioning. Static conditioning revealed that bamboo fibre reinforced composites show a smaller decrease in Young’s modulus with moisture content than other natural fibre reinforced composites such as for example flax based composites. The behaviour is explained by the chemical composition of the fibre and demonstrated by dynamic mechanical analysis that illustrates how composites made with fibres of high lignin content retain their glass transition temperature in moist conditions. The influence of hygroscopic cycling was also assessed, with emphasis on the influence of the remaining parenchyma on the fibre surface. Clean fibres, are beneficial for the long term behaviour, with less deterioration in properties. Porosity analysis was performed via X-ray computed tomography to provide insight into the material structure of the composite and the effects of hygroscopic cycling.

A flexible lead-free piezoelectric nanogenerator based on vertically aligned BaTiO3 nanotube arrays on a Ti-mesh substrate

Abstract: A uniform piezoelectric film on a flexible substrate is highly desirable for the construction of mechanical energy harvesting devices and self-powered sensors. In this study, we synthesized piezoelectrically active tetragonal phase BaTiO3 (BTO) nanotube arrays uniformly coated on a flexible Ti-mesh substrate by in situ conversion of anodized TiO2 nanotubes using a low temperature hydrothermal process. The direct conversion of the TiO2 nanotube to tetragonal phase BTO provides an excellent way to make flexible composites with a uniform distribution and enhanced volume fraction of piezoelectrically active BTO film. Based on the merits of the tetragonal phase BTO film on a Ti-mesh substrate, a novel fully bendable and mechanically robust piezoelectric nanogenerator (PENG) was fabricated. The oriented tetragonal phase BTO nanotube film on the Ti-mesh substrate was encapsulated in a polydimethylsiloxane (PDMS) elastomeric layer and assembled between two indium tin oxide (ITO) coated polyethylene terephthalate (PET) electrodes to form a flexible PENG. The PENG device can harvest mechanical energy from repeated bending and releasing motions. The resulting output voltage and current reached up to 10.6 V and 1.1 μA, respectively. The output power generated was sufficient to instantaneously light a full screen liquid crystal display (LCD). The Ti-mesh/BTO-based PENG device is lead-free and does not have a toxic dispersion enhancer. It is a promising candidate for self-powered sensors and biomedical device applications.

Hydromagnetic stagnation point flow of a magnetite ferrofluid past a convectively heated permeable stretching/shrinking sheet in a Darcy–Forchheimer porous medium

Abstract: In this study, a two-dimensional magnetohydrodynamic stagnation point flow of magnetite ferrofluid past a stretching/shrinking sheet through a Darcy–Forchheimer porous medium is investigated in the occurrence of viscous dissipation, suction/injection, and convective heating. Using appropriate similarity transformations the governing nonlinear partial differential equations are transformed into a system of nonlinear ordinary differential equations, and then solved numerically using the shooting technique. Numerical results are obtained for dimensionless ferrofluid velocity, ferrofluid temperature, skin friction, and Nusselt number. The effects of various physical parameters on these quantities are investigated and presented in graphs and tables. The results indicate that dual solutions exist for the shrinking sheet. Stability analysis is performed to identify the stable solutions. It is found that the upper branch solution is hydrodynamically stable and physically achievable, whereas the lower branch solution is unstable and physically unrealistic. The fluid flow stability is maintained by increasing the magnetite nanoparticle volume fraction, suction/injection, and the magnetic field parameter. On the contrary, the porous medium parameter and porous medium inertia parameter inflates the flow stability. The heat transfer rate intensifies with the magnetite nanoparticle volume fraction and reduces with the porous resistance term.

COVID-19 lockdown impacts on heavy metals and microbes in shallow groundwater and expected health risks in an industrial city of South India

Abstract: In this investigation, the positive impact of COVID-19 lockdown on heavy metals concentration and biological parameters in the shallow groundwater samples of Coimbatore city of South India was ascertained. The groundwater samples (n=15) were obtained from shallow open wells during before lockdown (24–25 February 2020) and after lockdown (2–3 June 2020) periods. These samples were analysed for heavy metals (Fe, Mn, Ni, Cr and Pb) and biological parameters (E. coli, Fecal coliforms, Fecal streptococci and Total coliforms). Fe concentration was within the permissible limit but, the concentrations of Mn, Ni, Cr and Pb were above the allowable limits for drinking uses as per the WHO. However, after lockdown the number of samples crossing the cutoff limit had considerably decreased (Mn: from 2 to 0 mg/L; Ni: from 13 to 10 mg/L; Cr: 7 to 5 mg/L and Pb: from 13 to 8 mg/L). The heavy metal pollution index (HPI) revealed that 176.75 km2 (67.4%) and 85.35 km2 (32.6%) areas fell under unsuitable and very poor categories, respectively, during the pre-lockdown period, whereas 138.23 km2 (52.6%), 118.98 km2 (45.3%) and 4.89 km2 (2.1%) areas fell under very poor, poor and good categories, respectively, during the post-lockdown period. Similarly, Total coliform, Fecal coliform and E. coli had decreased distinctly due to the pandemic lockdown. Therefore, the shutdown of small and large-scale industries during the lockdown period had improved the groundwater quality. The health risk assessment showed that 93%, 87% and 80% of pre-lockdown samples, and 87%, 80% and 73% of post-lockdown samples possessed non-carcinogenic risks (HI > 1) for children, female and male categories, respectively.

Material design with the concept of solid solution-type defect engineering in realizing the conversion of an electrocatalyst of NiS2 into a photocatalyst for hydrogen evolution

Abstract: The conversion of a lower-bandgap and electrocatalyst-type NiS2 phase into a higher-bandgap and photocatalyst-type one with excellent photocatalytic hydrogen evolution reaction (PHER) is demonstrated. In- and O-added NiS2 (NiInOS) extended its bandgap for harvesting visible light and showed as a distorted pyrite structure with a molecular formula of (Ni0.872In0.128)[(O0.2S0.8)1.5(□)0.5]. (Ni,In)(O,S)2-x with active oxygen vacancy and a partial Ni3+-to-Ni2+ conversion achieves excellent PHER. The best (Ni,In)(O,S)2-x with an oxygen vacancy content of 16.8 % could produce 496.8 μmol/h H2 under visible light, while it was 7.63 μmol/h H2 at a content of 2.12 %. The DFT calculation predicts that surface oxygen vacancies of (Ni,In)(O,S)2-x have a strong interaction with H2O to reach a high water adsorption energy of -0.896 eV. Here, the conversion of NiS2 into photocatalyst indicates that defect engineering by forming solid solution with incorporation of indium and oxygen to have bimetal and bichalcogen (Ni,In)(O,S)2-x is a promising approach for novel materials design to extend material application.