Thermal instability in a rotating porous layer saturated by a non-Newtonian nanofluid with thermal conductivity and viscosity variation

The stability of a non-Newtonian nanofluid saturated horizontal rotating porous layer subjected to thermal conductivity and viscosity variation is investigated using linear and nonlinear stability analyses. The model used for the non-Newtonian nanofluid includes the effects of Brownian motion and thermophoresis. The Darcy law for the non-Newtonian nanofluid of the Oldroyd type is used to model the momentum equation. The linear theory based on the normal mode method, and the criteria for both stationary and oscillatory modes are derived analytically. A weak nonlinear analysis based on the minimal representation of truncated Fourier series method containing only two terms is used to compute the concentration and thermal Nusselt numbers. The results obtained during the analysis are presented graphically.     

Developments in photocatalytic antibacterial activity of nano TiO<Subscript>2</Subscript>: A review

TiO₂, which is one of the most explored materials, has emerged as an excellent photocatalyst material for environmental and energy fields, including air and water purification, self-cleaning surfaces, antibacterial and water splitting. This review summarizes recent research developments of TiO₂-based photocatalyst used for photocatalytic antibacterial applications. Several strategies to enhance the efficiency of TiO₂ photocatalyst are discussed, including doping with metal ions, noble metals, non-metals, and coupling with other materials. The mechanism of photocatalytic antibacterial activity in the presence of nano-sized TiO₂ is also discussed. The modified TiO₂ photocatalyst significantly inhibits the growth of bacterial cells in response to visible light illumination. TiO₂ photocatalysis appears to be promising as a route of advanced oxidation process for environmental remediation.     

Local structure studies of Ni doped ZnO/PVDF composite free-standing flexible thin films using XPS and EXAFS studies

Free-standing flexible films of Ni-ZnO/PVDF with three Ni concentrations were obtained by sol–gel technique. The as-deposited and the poled composite Ni-ZnO/PVDF films contained three different amount of Ni doping in ZnO nanocrystals as Zn_1?x Ni _x O (x?=?0.01, 0.04, and 0.09). XANES, XPS measurements have been carried out to investigate the valence states of the host and dopant ions in samples while local environments surrounding Zn and Ni sites have been critically examined using extended EXAFS and XPS measurements to throw a clear insight on the bonding environment in the Ni-ZnO/PVDF films     

The Role of Rubidium in Multiple‐Cation‐Based High‐Efficiency Perovskite Solar Cells

Perovskite solar cells (PSCs) based on cesium (Cs)‐ and rubidium (Rb)‐containing perovskite films show highly reproducible performance; however, a fundamental understanding of these systems is still emerging. Herein, this study has systematically investigated the role of Cs and Rb cations in complete devices by examining the transport and recombination processes using current–voltage characteristics and impedance spectroscopy in the dark. As the credibility of these measurements depends on the performance of devices, this study has chosen two different PSCs, (MAFACs)Pb(IBr)₃ (MA = CH₃NH₃⁺, FA = CH(NH₂)₂⁺) and (MAFACsRb)Pb(IBr)₃, yielding impressive performances of 19.5% and 21.1%, respectively. From detailed studies, this study surmises that the confluence of the low trap‐assisted charge‐carrier recombination, low resistance offered to holes at the perovskite/2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9‐spirobifluorene interface with a low series resistance (R_s), and low capacitance leads to the realization of higher performance when an extra Rb cation is incorporated into the absorber films. This study provides a thorough understanding of the impact of inorganic cations on the properties and performance of highly efficient devices, and also highlights new strategies to fabricate efficient multiple‐cation‐based PSCs.     

Design and Construction of a Helical Resonator for Delivering Radio Frequency to an Ion Trap

Supplying high voltage radio frequency (RF) is a critical part of ion trapping system due to impedance mismatching between RF source and the ion trap. A helical resonator has been constructed in order to deliver narrow bandwidth and high voltage RF to the ion trap for stable confinement of ions. The performances of the helical resonator have been studied for different capacitive load of the ion trap. Both the resonant frequency and quality factor of the resonator show strong dependence on external capacitive loads.     

Synthesis and study of structural,dielectric, magnetic and magnetoelectric properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–CoMn<Subscript>0.2</Subscript>Fe<Subscript>1.8</Subscript>O<Subscript>4</Subscript> composites

Magnetoelectric (ME) composites consisting of K_0.5Na_0.5NbO₃ (KNN) as ferroelectric phase and CoMn_0.2Fe_1.8O₄ (CMFO) as ferrite phase with general formula (x) CoMn_0.2Fe_1.8O₄–(1???x) K_0.5Na_0.5NbO₃ (x?=?10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant (\(\varepsilon ^{\prime}\)) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2P_r) and coercive field (2E_c) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (α_ME) has been measured. The maximum value of α_ME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.     

Microstructural and surface morphological studies on Co doped ZnS diluted magnetic semiconductor thin films

Microstructural and surface morphological studies of Co (2.5%) doped ZnS thin films deposited at different substrate temperatures (T_S) of 200, 400 and 600 °C by means of pulsed laser deposition are presented. The deposited films are in wurtzite-hexagonal crystal structure as confirmed by X-ray diffraction and Raman spectroscopy techniques. The films deposited at higher T_S show columnar morphology, as evidence by transmission electron microscopy measurements. Images of the surface topography have been taken by atomic force microscopy (AFM) for the film deposited at different T_S. The film deposited at T_S of 200 °C shows cone-like structures while deposited at T_S of 400 and 600 °C show columnar structures. A fractal analysis has been performed on AFM images to understand the microstructure and surface morphology of thin film at different T_S. Fractal analysis also reveals the morphological changes in the film with increasing T_S. The observed ferromagnetism is correlated with columnar growth of the film which can be used as diluted magnetic semiconductor for spintronic applications.     

70 years of Elastohydrodynamic Lubrication (EHL): A Review on Experimental Techniques for Film Thickness and Pressure Measurement

Elastic deformation of surfaces and piezo-viscous effect of lubricant make EHL a very complex lubrication regime. Elastohydrodynamic Lubrication becomes much more complex when conditions like rough surfaces, non-newtonian behavior of lubricant and temperature dependent flow are considered. The present paper takes the task of reviewing experimental methods applied till date for measuring film thickness and pressure. The paper has been divided into many sections and sub-sections to deal with these techniques in a lucid manner. Experimental methods have been categorized into Electrical, Optical and Acoustic methods. The difference of 8–10% between theoretical and experimental results are witnessed using Electrical methods. Whereas, this difference is less than 1% using Optical methods. Among all optical methods, Relative Optical Interference Intensity Technique is the most effective technique with an ability to measure the film thickness as small as 1 nm or less. The last section of the paper deals with the scope of improvement in measurement techniques in future to understand EHL in more detail.     

Densification and microstructural evolution of spark plasma sintered NiTi shape memory alloy

The effect of particle size and sintering temperature on the densification and microstructural characteristics of nickel-titanium shape memory alloy (NiTi-SMA) has been investigated using spark plasma sintering (SPS) process. The Ni and Ti elements in different particle sizes were alloyed in the composition of Ni_50.6Ti_49.4. The milled NiTi powders were consolidated using SPS process in a temperature range of 700–900?°C. The densification was characterized by plotting temperature, current and relative displacement of punch as a function of holding time. The results showed that a maximum relative density of ～98% can be achieved for NiTi-SMA with an average particle size of 10?µm at a sintering temperature of 900?°C. The microstructure of the sintered NiTi-SMA was examined using scanning electron microscope (SEM) and composition of NiTi alloy was analyzed using energy dispersive spectroscopy (EDS) analysis. The effect of sintering temperature on the microstructural evolution and transformation was also studied.     

Removal of Cu(II) and Pb(II) by Pithophora oedogonia: sorption, desorption and repeated use of the biomass

Maximum sorption of Cu(II) and Pb(II) by dried filamentous green alga Pithophora oedogonia occurred at pH 4.5 and 5.0, respectively. Chemical pretreatment could not appreciably enhance the metal sorption ability of the biomass. HCl and EDTA desorbed 92-96% of the sorbed metal from the metal-loaded biomass. Sorption and desorption of both the test metals were very rapid attaining an equilibrium within 15 min. The time course data of both the processes fitted well to the pseudo-first and the pseudo-second-order Lagergren kinetic models with r2> or =0.979. The isotherm equilibrium of Cu(II) and Pb(II) followed the Redlich-Peterson and Sips model very well with r2> or =0.991. The sorption of Cu(II) and Pb(II) at varying biomass doses could be well defined by linear and hyperbolic decrease, respectively. The regenerated biomass of Pithophora has better reusability for Pb(II) than for Cu(II). A good mechanical strength of Pithophora biomass was apparent as only 10-15% loss of biomass occurred at the end of the fifth cycle.