Low sintering effect on structural,electrical and magnetic properties of rare-earth metal ion Er3+-substituted nickel–zinc spinal ferrites

Journal of Materials Science: Materials in Electronics - The nano-crystalline particles of erbium-substituted Ni–Zn ferrites with compositional formula Ni0.7Zn0.3ErxFe2?xO4...     

Decision support system based on a hybrid genetic algorithm–Kohonen map for combined mode conduction–radiation heat transfer in a porous medium: A comparative assessment of three variations of the Kohonen map

A hybrid genetic algorithm (GA)–Kohonen map, with its three variants, is explored for the first time for the decision-making system in a porous ceramic matrix (PCM)-based burner through determination of the regime of operation. Four different attributes of PCMs such as convective coupling (P₂), extinction coefficient (β), downstream porosity (ϕ₂), and scattering albedo (ω) are selected for determining the regime of operation of a PCM-based burner. Changes in any of these attributes of a PCM lead to significant changes in the temperature profiles of the gas and solid phases. Temperature profiles of the gas and solid phases are computed by developing a numerical model. Various samples corresponding to different regimes are generated and used in a hybrid GA–Kohonen map. The best architectural details such as the neuron number and training epochs are obtained from GA as output. The best Kohonen map is trained with the input data, and regimes of operation for new temperature profiles are predicted. A supervised Kohonen map is able to provide the highest average class prediction of more than 40%. All the variants are assessed under two different types of neuron grids: hexagonal and rectangular. Comparative assessments of the three different variants of Kohonen maps, in terms of CPU time and average class prediction, are carried out.     

Emission (Gd3+ and Sm3+) and ESR (Gd3+) studies of La1−xLnxB3O6 (Ln = Gd,Sm; 0 ≤ x ≤ 0.2 for Gd; 0 ≤ x ≤ 0.1 for Sm) phosphors

Polycrystalline powders of rare-earth doped La_1?xGd_xB₃O₆ (0?≤?x?≤?0.2) and La_1?xSm_xB₃O₆ (0.0?≤?x?≤?0.1) phosphors were successfully prepared by a B₂O₃ flux method. All the phosphor samples are well characterized by powder X-ray diffraction (XRD), infrared (IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) methods and fluorescence lifetime of Sm³⁺ ion. The XRD patterns show that La_1?xM_xB₃O₆ (M?=?Gd and Sm) adopt monoclinic with the I2/a space group. The SEM–EDS results confirmed the doping of Gd and Sm into LaB₃O₆ lattice. The IR and Raman spectra of these solid solutions gave distinctive bands corresponding to planar BO₃ and tetrahedral BO₄ groups. The photoluminescence (PL) spectra of La_1?xGd_xB₃O₆ gave a strong emission band, ⁶P_J?→?⁸S_7/2, at 310 nm. The PL spectra of La_1?xSm_xB₃O₆ phosphor showed orange-red emission at 598 nm when excited using light of wavelength of 402 nm. The results were obtained by the transition ⁴G_5/2?→?⁶H_7/2 of Sm³⁺ ions. The influence of dopant concentration on the emission profiles was studied. The ESR spectra of La_1?xGd_xB₃O₆ (x?=?0.02) gave a typical U-spectrum and spin-Hamiltonian parameters are deduced.

     

Assessment of heat transfer in large parallel plates with a narrow gap maintained at a constant temperature

Investigations are conducted on electromagnetohydrodynamic (EMHD) flow and heat transfer in a third-grade fluid flowing through large parallel plates, which are maintained at constant temperatures. The impact of convective heat transmission is disregarded since the space between the plates is small. The influence of viscous dissipation is considered. Despite being addressed for Newtonian fluids, the conduction problem with the viscous dissipation effect is not examined in third-grade fluids for EMHD flow and heat transfer behavior. The least-square method is adopted to solve nondimensional, nonlinear momentum and energy conservation equations to get the dimensionless velocity, temperature distribution, and heat flux. Temperature and heat flux are investigated in relation to the third-grade fluid parameter, the Hartmann number, the electric field parameter, and the Brinkman number. The findings show a rise in the Brinkman number dramatically increases heat transfer from both walls, necessitating cooling of both plates. The heat flow from both walls increases as the parameters of third-grade fluid increases.