M. Awais

Dye sensitised solar cells with nickel oxide photocathodes prepared via scalable microwave sintering

Photoactive NiO electrodes for cathodic dye-sensitised solar cells (p-DSCs) have been prepared with thicknesses ranging between 0.4 and 3.0 μm by spray-depositing pre-formed NiO nanoparticles on fluorine-doped tin oxide (FTO) coated glass substrates. The larger thicknesses were obtained in sequential sintering steps using a conventional furnace (CS) and a newly developed rapid discharge sintering (RDS) method. The latter procedure is employed for the first time for the preparation of p-DSCs. In particular, RDS represents a scalable procedure that is based on microwave-assisted plasma formation that allows the production in series of mesoporous NiO electrodes with large surface areas for p-type cell photocathodes. RDS possesses the unique feature of transmitting heat from the bulk of the system towards its outer interfaces with controlled confinement of the heating zone. The use of RDS results in a drastic reduction of processing times with respect to other deposition methods that involve heating/calcination steps with associated reduced costs in terms of energy. P1-dye sensitized NiO electrodes obtained via the RDS procedure have been tested in DSC devices and their performances have been analysed and compared with those of cathodic DSCs derived from CS-deposited samples. The largest conversion efficiencies (0.12%) and incident photon-to-current conversion efficiencies, IPCEs (50%), were obtained with sintered NiO electrodes having thicknesses of ~1.5-2.0 μm. In all the devices, the photogenerated holes in NiO live significantly longer (τ(h) ~ 1 s) than have previously been reported for P1-sensitized NiO photocathodes. In addition, P1-sensitised sintered electrodes give rise to relatively high photovoltages (up to 135 mV) when the triiodide-iodide redox couple is used.

The influence of slip condition on thin film flow of a fourth grade fluid by the homotopy analysis method

This paper provides an investigation regarding slip effects on thin film flow of a fourth grade fluid down a vertical cylinder. The nonlinear problem that arises is solved for both exact and HAM (homotopy analysis method) solutions. Exact and HAM solutions are also compared. Finally we briefly describe the flow characteristics to include the effects of emerging parameters.

Unsteady Squeezing Flow of Jeffery Fluid between Two Parallel Disks

We investigate an unsteady axisymmetric flow of a Jeffrey fluid between two parallel disks. The relevant partial differential equations are modeled and simplified by using appropriate transformations. The resulting ordinary differential system is solved and a series solution is obtained. Effects of various parameters of interest on the flow quantities are seen. It is found that the velocity profile increases when porosity and squeezing parameters are increased.

Raman Spectroscopy of Natural Bone and Synthetic Apatites

Abstract Raman spectroscopy of natural bones and hydroxyapatites is described. In addition, how Raman spectroscopy has proved crucial in providing baseline data for the modification of synthetic apatite powders that are routinely used now as bone replacement materials is explained. It is important to understand the chemical structural properties of natural bone. Bone consists of two primary components: an inorganic or mineral phase, which is mainly a carbonated form of a nanoscale crystalline calcium phosphate, closely resembling hydroxyapatite, and an organic phase, which is composed largely of type I collagen fibers. Other constituents of bone tissue include water and organic molecules such as glycosaminoglycans, glycoproteins, lipids, and peptides. Ions such as sodium, magnesium, fluoride, and citrate are also present, as well as hydrogenophosphate. Hence, the mineral phase in bone may be characterized essentially as nonstoichiometric substituted apatite. Such a distinction is important in the development of synthetic calcium phosphates for application as skeletal implants. An understanding of bone function and its interfacial relationship to an implant clearly depends on the associated structure and composition. Therefore, it is essential to fully understand the chemical composition of bone, and Raman spectroscopy is an excellent technique for such an analysis.

Convective heat transfer analysis for MHD peristaltic flow in an asymmetric channel

Magnetohydrodynamic peristaltic flow of Jeffery fluid in an asymmetric channel is addressed. The channel walls satisfy the convective conditions. Asymmetry here is considered due to wave trains of different amplitudes and phases. Solutions for the velocity, temperature and pressure gradient are obtained using long wavelength approximation. Plots reflecting the impact of various parameters of interest are shown and examined.

Effects of viscous dissipation on MHD boundary layer flow of Sisko fluid over a stretching cylinder

The present study concentrates on the analysis of magnetohydrodynamic boundary layer flow of Sisko fluid over continuously stretching cylinder. The viscous dissipation effect is assumed in heat equation. To modify the governing equations first boundary layer approximations are applied. After this simultaneous partial differential equations are converted into the ordinary differential equations by applying proper similarity transformations. To find the numerical solution of this system of ordinary differential equations shooting method is utilized. Graphs are plotted to figure out the characteristics of physical parameters on momentum and heat equations. The variations of all physical parameters on skin friction coefficient and local Nusselt number are displayed via figures and tables.

Numerical solution of MHD Sisko fluid over a stretching cylinder and heat transfer analysis

Purpose – The purpose of this paper is to examine the Sisko fluid model over a stretching cylinder with heat transfer and magnetohydrodynamics. Design/methodology/approach – The boundary layer approach is employed to simplify the governing equations. Suitable similarity transformations are used to transform the governing partial differential equations into ordinary differential equations. In order to solve this system of ordinary differential equations numerically, shooting method in conjunction with Runge-Kutta-Fehlberg method is used. Findings – The effects of physical parameters involved in velocity and temperature profiles are shown through graphs. It is observed that Sisko fluid parameter and curvature parameter enhances fluid velocity while motion of fluid is retarded by increasing magnetic field strength. Additionally temperature of fluid raise with curvature parameter while it fall down for larger values of Prandtl number. Skin friction coefficient and Nusselt number are computed and presented in ...

Stagnation point flow of Burgers' fluid over a stretching surface

The steady flow of an incompressible Burger fluid near a stagnation-point over a linearly stretching surface is investigated. The two-dimensional flow equations are modelled and then simplified by employing boundary layer analysis. The solution to the arising nonlinear problem is computed in the whole spatial domain (0 ≤ η< ∞). Interpretation of various emerging parameters is given through graphs for velocity and temperature fields. Furthermore tables are constructed in order to make a comparative study with the previous published results. Comparison shows an excellent agreement with the previous limiting investigations in the field.

Homogeneous-heterogeneous reactions in Williamson fluid model over a stretching cylinder by using Keller box method

This paper addresses the effect of homogeneous-heterogeneous reaction on Williamson fluid model over a stretching cylinder. The boundary layer partial differential equations are converted into ordinary differential equation by using suitable transformations. The non-linear ordinary differential equations are solved by using implicit finite difference Keller box technique. The effects of several pertinent parameters on velocity, temperature and concentration profiles are deliberated graphically. The behavior of skin friction coefficient and Nusselt number are examined through graphs.

MASS TRANSFER EFFECTS ON THE UNSTEADY FLOW OF UCM FLUID OVER A STRETCHING SHEET

This paper looks at the mass transfer effects on the unsteady two-dimensional and magnetohydrodynamic flow of an upper-convected Maxwell fluid bounded by a stretching surface. Homotopy analysis method is used for the development of series solution of the arising nonlinear problem. Plots of velocity and concentration fields are displayed and discussed. The values of surface mass transfer and gradient of mass transfer are also tabulated.