Women University of Azad Jammu & Kashmir

This investigation presents a comprehensive sensitivity analysis to optimize heat transfer parameters in magnetohydrodynamic (MHD) bioconvective flow of a Casson nanofluid across an axisymmetric rotating disk embedded in a Darcy-Forchheimer porous medium. Heat transfer in nanofluids increases thermal management efficiency in applications including energy storage, cooling technologies, and complex bioengineering systems. Because it accounts for the effects of magnetic fields, bioconvection brought on by motile microorganisms, activation energy, and non-Newtonian Casson rheology, which exhibits shear-thinning behavior, the flow model is relevant to these domains. The dynamics of nanoparticles are described using the Buongiorno model, which accounts for thermophoresis and Brownian motion. Using appropriate similarity transformations and boundary layer approximations, the governing nonlinear partial differential equations defining velocity, energy, nanoparticle concentration, and microbe density are reduced to a connected set of ordinary differential equations. The resulting boundary value problem is numerically solved using MATLAB's bvp4c solver. The effects of key parameters (Casson fluid parameter, Eckert number, and thermal radiation) on the rate of heat transfer are systematically examined using sensitivity analysis and through response surface methodology (RSM) with a central composite design. The investigation indicates that the heat source/sink parameter, thermophoresis, and temperature ratio factor significantly enhance the thermal boundary layer and temperature distribution. The velocity field accelerates with increasing mixed convection parameters but decelerates in a magnetic field. Analysis of the microorganism profile reveals a decelerated trend for the microorganism difference parameter, bioconvection Lewis, and Peclet number. Furthermore, the heat transfer rate is more sensitive to the Eckert number.

Silver nanomaterials are of significant interest due to their unique characteristics, including high reactivity, a high specific surface area, and small size, which make them important in various industrial applications, such as medicine, food, consumer products, and healthcare. In this study, silver nanoparticles are synthesized using atmospheric pressure microplasma, an eco-friendly technique, with silver nitrate (AgNO3) as the precursor and fructose as a natural stabilizing agent. The influence of reaction time (25, 35, and 45 min) on the structural characteristics of nanoparticles, functional properties, and their antibacterial and antifungal activities is investigated. The X-ray diffraction analysis reveals the synthesis of pure face-centered cubic (FCC) silver phases, with no secondary phases present. The peaks become broader with increasing reaction time, whereas the crystalline size decreases. Due to quantum confinement effects, UV–visible spectroscopy shows clear surface plasmon resonance peaks and an increase in the energy band gap from 3.20 to 3.47 eV with increasing reaction time. Scanning electron microscopy, combined with particle size distribution analysis, reveals that longer treatment times consistently yielded smaller particles, with sizes of 31.12 nm, 25.98 nm, and 22.24 nm, respectively. The presence of functional groups and Ag–O bonding, which support particle stability, is verified by FTIR and Raman spectroscopy. Significant inhibition zones (up to 30 mm) are observed in antibacterial and antifungal assays, and the higher surface reactivity of smaller nanoparticles is associated with enhanced bioactivity. This study demonstrates that adjusting the reaction time allows for control over the crystallite characteristics and antimicrobial activity of silver nanoparticles.

In this work, a two-step process to improve Hardox 450's surface behavior was used. First, the Pechini method was used to put xerogel coatings with Ni nanoparticles on (i) the unmodified substrate (SURNi) and (ii) systems with 0.002 g (SURG2) and 0.008 g (SURG8) of Ni/graphene oxide (Ni/GO). Second, the base metal (BM) and coated samples were treated with optimized micro-laser treatment parameters. High-resolution TEM showed that spherical Ni nanoparticles were forming on and between flakes made from graphene. This confirmed how nucleation and growth happen in the hybrid xerogels. In pin-on-disc tests with a 6 N load and a sliding distance of 1000 m, SURG8 showed the least volumetric wear (0.18 mm3) of all the conditions. This behavior is linked to its high storage modulus (2.7 GPa) and contact stiffness (577.59 N/m) found by nanoindentation in DMA mode, as well as the lubricating effect of the graphene-based phase found by Raman spectroscopy. EBSD analysis also showed that fine equiaxed grains with better orientation were encouraged. The combined effect of Ni nanoparticles, graphene-derived structures, and micro-laser processing strengthened the surface, leading to better tribomechanical performance.

Green synthesis emerged as an effective approach for the eco-friendly synthesis of nanoparticles with improved biological applications. This study assesses the potential of root extract of Swertia cordata for the green synthesis of silver nanoparticles and examines their antimicrobial and antioxidant properties. Different analytical techniques such as UV-visible spectroscopy, Zeta potential, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) analysis, were employed to characterize silver nanoparticles. The formation of silver nanoparticles was initially verified using UV-visible spectroscopy, which exhibited a characteristic absorption peak at 454 nm. XRD analysis revealed the face-centered cubic (FCC) crystalline structure. The zeta potential of -35 mV indicated the highest colloidal stability due to repulsion between the particles. The DLS confirms that the particle size distribution was between 80 and 120 nm. EDX analysis detected silver as the highest amount in the sample. The biosynthesized silver nanoparticles exhibit remarkable antibacterial activity against both Gram-negative bacteria and Gram-positive bacteria. The largest zone of inhibition was observed against Streptococcus pneumoniae (29 +/- 1.5 mm) at a dose of 0.9 mg/mL. The synthesized silver nanoparticles also showed efficient and strong antifungal activity against two fungal strains, viz., Penicillium nutatum and Rhizopus stolonifera. The free radical scavenging activity of the synthesized silver nanoparticles was highest (69.5%) at 50 ppm of AgNPs concentration. The results confirm that silver nanoparticles synthesized from S. cordata root extract exhibited remarkable antimicrobial and antioxidant potential, making it therapeutic alternative for treating several diseases.

This study analyzes the impact of thermal radiation on the bioconvective flow of a nanofluid over a radially expanding sheet embedded in a Darcy-Forchheimer porous medium. Bioconvection based on gyrotactic microorganisms is crucial for biotechnology and biosensor applications. The primary objective of bioconvection research is to improve energy and mass transmission, which has significant implications for chemical, mechanical, civil, electrical, and process intensification engineering. This work develops a new mathematical model for the unsteady bioconvective flow of a chemically reactive magnetohydrodynamic (MHD) nanofluid with nonlinear thermal radiation and gyrotactic microorganisms in the presence of Darcy-Forchheimer effects. The governing equations include solar radiation, viscous dissipation, and the Buongiorno model in addition to thermophoresis and Brownian motion. A suitable similarity transformation is used to reduce the controlling partial differential equations to a set of ordinary differential equations. The integrated MATLAB solver BVP4C is used to numerically solve these linked higher-order equations for various values of the governing parameters once they have been transformed into a system of first-order ODEs. The results, which are presented graphically, demonstrate significant variations in the motile microbe density, Nusselt number, and skin friction coefficient. It is discovered that increasing the thermophoresis and radiation parameters enhances the fluid temperature, while increasing the Darcy-Forchheimer parameter causes a decrease in wall shear stress.