Volume 74, Issue 12

A facile synthesis of undoped and 2.0 % selenium-doped zinc oxide nanoparticles (NPs) was efficaciously accomplished through a mechanochemical route using zinc acetate dihydrate, oxalic acid, and Se powder in a solid state reaction. After calcination at 450 °C, the obtained nanostructures were probed by X-ray diffraction, where the acquired data revealed the pertinence of the wurtzite hexagonal ZnO for both undoped (ZnO) and doped (Se/ZnO) NPs and crystallite sizes of 30 and 24 nm for ZnO and Se/ZnO, respectively. The formation of the target NPs was confirmed by the scanning and transmission electron microscopy, energy-dispersive X-ray analysis, and the Fourier transformation infrared molecular vibrations data. The porosity investigations indicated 33.65 m 2 /g Brunauer–Emmett–Teller surface area, 197 Å pore diameter, and 0.172 cm 3 /g pore volume for the Se/ZnO NPs compared to lower values for the pristine ZnO. The band gap energies were 3.19 and 3.15 eV for ZnO and Se/ZnO as perceived from the Tauc plots of the UV-visible absorption measurements. The photodegradation of methylene blue dye under UV illumination was found to follow the pseudo–first-order kinetics with an enhanced performance by the doped samples as reflected by the higher (3.2 × 10 −3 s −1 ) rate constant relative to the undoped sample (1.7 × 10 −3 s −1 ). A photodegradation mechanism was suggested in the light of the band gap energy investigation. The obtained findings indicate the improvement of ZnO properties by doping with Se through a simplistic and inexpensive approach.

We considered a steady flow of viscous incompressible fluid and solute transfer in an axisymmetric tube of uniform cross section with variable wall permeability, which is relevant to the study of movement of solute across the glomerular capillaries. The solutions for the nonlinear governing equations of the fluid flow and solute transfer are obtained by analytical/numerical methods. The combined effect of variable wall permeability and flow parameters on the hydrostatic pressure, osmotic pressure, velocity profiles, concentration profiles, and the total solute clearance are investigated and are presented in this paper. It is found that an increase in the variable permeability parameter increases the solute concentration at the wall.

We make a critical review of the semiclassical interpretation of quantum cosmology and emphasise that it is not necessary to consider that a concept of time emerges only when the gravitational field is (semi)classical. We show that the usual results of the semiclassical interpretation and its generalisation known as the Born–Oppenheimer approach to quantum cosmology can be obtained by gauge fixing, both at the classical and quantum levels. By “gauge fixing,” we mean a particular choice of the time coordinate, which determines the arbitrary Lagrange multiplier that appears in Hamilton’s equations. In the quantum theory, we adopt a tentative definition of the (Klein–Gordon) inner product, which is positive definite for solutions of the quantum constraint equation found via an iterative procedure that corresponds to a weak coupling expansion in powers of the inverse Planck mass. We conclude that the wave function should be interpreted as a state vector for both gravitational and matter degrees of freedom, the dynamics of which is unitary with respect to the chosen inner product and time variable.

The formation of capillary ridges is the typical features of thin viscous or viscoelastic fluids over a locally heated plate. This ridge leads to the nonuniformity in the thin film coating. In this work, the formation of capillary ridges on the free surface of thin second-grade non-Newtonian fluid flowing over an inclined heated plate is discussed. The flow is modelled by two-dimensional laws of conservation of mass, momentum, and energy with corresponding boundary conditions at the plate and the free surface. An evolution equation for the description of the liquid thin film height is derived from the two-dimensional balance equations using the long-wave approximation. The resulting nonlinear dynamic equation is discretised implicitly on a uniform grid using the finite volume method. The obtained results on the capillary ridge in the free surface are discussed for the different flow parameters. It is noted that the capillary ridge height is higher for the second-grade viscoelastic fluid in comparison to the Newtonian one. This study can be a starting point to investigate the influence of second-grade viscoelastic parameter on the free surface instability and other phenomena of interest.

Novel green phosphors Zn 3 Al 2 Ge 2 O 10 : Mn 2+ were successfully synthesised at high temperature under weak reducing atmosphere. X-ray diffraction results indicate that the samples have like-spinel structure. The morphology, chemical states, and the composition of the dopants in the host were analysed with high-resolution transmission electron microscopy, energy dispersive spectrum, high-angle annular dark-field, and X-ray photoelectron spectroscopic techniques. The photoluminescence spectra show that the emission peak is at 537 nm (under excitation at λ ex = 334 nm), which is the strong green emission resulting from the 4 T 1 ( 4 G)- 6 A 1 ( 6 S) transition of Mn 2+ ion. The full width at half maximum broadband of the strongest broad emission is about 50 nm. The Zn 3 Al 2 Ge 2 O 10 doped with 4 mol% Mn 2+ appears to have the highest emission intensity after thermal treatment at 1250 °C for 5 h. The CIE coordinates are x = 0.279, y = 0.625, corresponding to green region, and the decay time is 4.88 μs. The results indicate that the phosphors may be used as a trichromatic fluorescent material.

A systematic first principles study has been carried on zinc oxide and their Cd-substituted ternary alloys in the zinc blende phase for the measurement of various thermodynamic parameters over a wide range of temperature (0–1200 K) and pressure (0–10 GPa). A significant change in various thermodynamic parameters of Cd-substituted ZnO has been noted. Cd-rich Cd x Zn 1−x O has the least thermal conductivity, bulk modulus and Debye temperature, whereas maximum molar heat capacities, Grüneisen parameter and entropy. The anharmonicity of the semiconducting system changes in response to temperature and pressure variation, which in turn control thermal expansion. Internal energy, free energy and entropy are more temperature sensitive as compared to pressure.

The present article comprises computation of elastic, ultrasonic, and thermo-physical properties of RM (R = Tb, Dy, Ho, Er, Tm; M = Zn, Cu) compounds at 300 K. The second-order elastic constants (SOECs) and elastic moduli are evaluated initially, using potential model approach considering interaction up to second nearest neighbours. The ultrasonic velocities are obtained for wave propagation along <100>, <110>, and <111> crystallographic directions using evaluated SOECs. The Debye temperature, specific heat at constant volume, thermal energy density, thermal conductivity, and thermal relaxation time are also calculated. The obtained results are compared and analysed for justification and application of materials.

The bandgap was tuned to investigate the electronic and optical aspects using first-principle calculations for solar cells and other optical applications. The bandgap range varies from 1.6 to 2.1 eV for Ga 1− x Al x As and from 0.8 to 1.5 eV for Ga 1− x Al x Sb ( x = 0.0, 0.25, 0.5, 0.75, 1.0). The dispersion, polarisation, and attenuation have been illustrated in terms of transparency and maximum absorption of light. The inversion of polarised atomic planes near the resonance allows the maximum absorption in ultraviolet to visible region. The Penn’s model (ε 1 (0) ≈ 1 + (ℏω p /E g ) 2 ) and optical relation ε1(0)${\varepsilon_{1}}\left(0\right)$ = n 2 (0) confirm the reliability of our finding. The maximum absorption, optical conduction, and minimum optical energy loss increase the credibility of the studied materials for energy storage device manufacture.