Enabling remote learning system for virtual personalized preferences during COVID-19 pandemic

Multimedia Tools and Applications - The education system worldwide has been affected by the Corona Virus Diseases 2019 (COVID-19) pandemic, resulting in the interruption of all educational...     

Experimental study on heat transfer and pressure drop of in-house synthesized graphene oxide nanofluids

Abstract

In this article, first, graphene oxide nanosheets were synthesized in-house according to the modified Hummers method, and these nanosheets were used to prepare graphene oxide nanofluids at two concentrations. Then the thermophysical properties of nanofluids were characterized using X-ray diffraction analysis, a scanning electron microscope, and UV–Vis spectrophotometry. The particle size distribution was investigated using dynamic light scattering. Then, a fundamental study was conducted on the thermal-hydraulic characteristics of graphene oxide nanofluids flowing through a straight copper tube. An experimental setup was developed to find the heat transfer characteristics and pressure drop of nanofluids in the test section consisting of a copper tube with constant heat flux. The flow regimes and associated pressure drop and heat transfer characteristics at varying flow rate were investigated at three different heat flux conditions of 7.4, 9.1, and 12.6?kW/m². Due to the increase in viscosity, flowrate and Reynolds number decreased from 0.01 to 0.1?wt% of graphene oxide nanofluids at constant pump frequency. Experimental data obtained for water were validated with the findings from the literature, and the correlations were formulated for the Nusselt number and Reynolds number by considering the multiple regression analysis. The convective heat transfer coefficient for graphene oxide at 0.01?wt% was higher when compared to graphene oxide at 0.1?wt% and water. The variation of Nusselt number with the heat flux and velocity was insignificant.     

Effect of uniaxial drawing on the structure and glass transition behavior of poly(trimethylene 2,6-naphthalate)/layered clay nanocomposites

The structure–property relationships of poly(trimethylene 2,6-naphthalate)/layered clay nanocomposites are being investigated under uniaxial drawing by using synchrotron wide angle X-ray diffraction, small angle X-ray scattering, transmission electron microscope and dynamic mechanical analyzer. The cold crystallization at 110 °C of PTN and nanocomposites samples under drawing induced the α-crystal form with the chain axis (c-axis) aligned along the drawing direction as well as parallel to the layered clay surface. However, the broad surfaces of the layered clay are oriented and rotated nearly perpendicular to the sample's surface, forming the house of cards type structure. Such structural formation of layered clay in the PTN matrix influenced the thermomechanical properties depending on the extent of confinement and surface interaction effects. The amorphous and crystallized structures of the nanocomposites showed the analogous tendency in which T_g decreased and increased before and after drawing, respectively, relative to the neat PTN. Despite the evolution of free volume after drawing, the nanocomposites exhibited an unusual positive shifting trend in T_g. The deviation of T_g in the PTN nanocomposites system is ascribed to the interplay of two competing effects; (i) the increase in the local free volume owing to the confining effect of intercalation (enhanced the chain mobility) and (ii) entropic constraint imposed by the stronger interfacial interaction due to the physical jamming of layered clay (retarded the chain mobility).     

Synthesis,Characterization, Antibacterial Properties,and In Vitro Studies of Selenium and Strontium Co-Substituted Hydroxyapatite

In this study, as a measure to enhance the antimicrobial activity of biomaterials, the selenium ions have been substituted into hydroxyapatite (HA) at different concentration levels. To balance the potential cytotoxic effects of selenite ions (SeO₃²⁻) in HA, strontium (Sr²⁺) was co-substituted at the same concentration. Selenium and strontium-substituted hydroxyapatites (Se-Sr-HA) at equal molar ratios of x Se/(Se + P) and x Sr/(Sr + Ca) at (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2) were synthesized via the wet precipitation route and sintered at 900 °C. The effect of the two-ion concentration on morphology, surface charge, composition, antibacterial ability, and cell viability were studied. X-ray diffraction verified the phase purity and confirmed the substitution of selenium and strontium ions. Acellular in vitro bioactivity tests revealed that Se-Sr-HA was highly bioactive compared to pure HA. Se-Sr-HA samples showed excellent antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus carnosus) bacterial strains. In vitro cell–material interaction, using human osteosarcoma cells MG-63 studied by WST-8 assay, showed that Se-HA has a cytotoxic effect; however, the co-substitution of strontium in Se-HA offsets the negative impact of selenium and enhanced the biological properties of HA. Hence, the prepared samples are a suitable choice for antibacterial coatings and bone filler applications.     

Cd transfer across water/1,2-dichloroethane microinterfaces facilitated by complex formation with 1,10-Phenanthroline

The transfer of Cd²⁺ facilitated by 1,10-Phenanthroline (phen) was investigated at the microinterface of two immiscible electrolyte solutions, hosted by a 25 μm diameter orifice of a micropipette. Cyclic voltammetry (CV) was employed to examine the transfer in the conditions of the ligand (organic phase) in excess and Cd²⁺ (aqueous phase) in excess. In these conditions, asymmetric (peak-shaped in the forward scan and steady state in the backward scan), and reversible steady state (for the two scan directions) voltammograms were observed. The dependence of half-wave potential on the ligand concentration suggested that the equilibrium was effectively displaced towards a 1:3 (Cd²⁺:ligand) stoichiometry, with a formation constant, β₃ = 3.9 × 10²⁹. The diffusion coefficients of Cd²⁺ in the aqueous solution and those of phen, Cd(phen)₃²⁺ in organic phase were evaluated to be 6.5 × 10⁻⁶, 5.8 × 10⁻⁶, and 5.1 × 10⁻⁶ cm² s⁻¹ respectively, using CV.