MHD mixed convection stagnation point flow of a hybrid nanofluid past a vertical flat plate with convective boundary condition

The steady magnetohydrodynamics (MHD) mixed convection stagnation point flow of a hybrid nanofluid past a vertical flat plate with convective boundary condition is investigated in this study. By choosing appropriate similarity variables, the partial differential equations are transformed into a system of linear equations which are solved afterwards by using the boundary value problem solver, namely bvp4c in Matlab software. The solutions of the ordinary differential equations are proven to have two branches which are upper and lower solutions in a certain range of the mixed convection parameter. This leads to the execution of a stability analysis that verifies the achievable solution of the upper branch which is considered stable while the lower branch is unstable. The findings exposed that the fluid velocity increases with the increasing value of the magnetic parameter while the fluid temperature is decreased contradictory.     

Electromagnetic absorption of SRR based double-inverse E-Shaped metamaterial for DCS,EESC, 5G,and WiMAX applications

Herein, a novel double-inverse E-structured resonator metamaterial (MTM) surrounded by split-ring resonators (SRRs) is introduced and proposed. The proposed MTM has working frequency ranges of 1.62 – 1.79 GHz, 2.08 – 2.21 GHz, 4.39 – 4.99 GHz, and 5.65 – 6.09 GHz. In addition, the proposed MTM can be applied in digital cellular system uplinks (DCS) (1.736 GHz), earth exploration-satellite communication (EESC) (2.148 GHz), lower band 5G (4.8 GHz), and WiMAX (5.89 GHz) applications. The electromagnetic radiation reduction performance of the proposed MTM is investigated at 900 MHz and 1800 MHz of GSM cellular bands. The Finite Integration Technique (FIT) based on high-frequency electromagnetic software is utilised for the development of design along with a detailed investigation of the MTM properties. The proposed MTM is formed by developing a double-inverse E-structure in the middle surrounded by SRRs. The resonator structure with SRRs is implemented on an epoxy resin FR4 substrate, which has a compact size of 11.11 × 11.11 mm². The unit cell has a high effective medium ratio of 14.82. Furthermore, the developed MTM shows a negative refractive index region from 3.124 to 6.98 GHz and double-negative region from 3.94 to 4.57 GHz, 5.26 to 5.49 GHz, and 6.29 to 6.88 GHz. In addition, SAR evaluation is also performed to test the competence of utilising the proposed MTM on modern mobile phones. The MTM has an electromagnetic absorption rate of about 44% and 43% at 900 MHz and 1800 MHz, respectively, for 1g whereas about 43% and 44% at 900 MHz and 1800 MHz, respectively, for 10g. Thus, the performance and characteristics of the developed MTM can be utilised for the above-mentioned applications.     

Steam-reforming of ethanol for hydrogen production

Production of hydrogen by steam-reforming of ethanol has been performed using different catalytic systems. The present review focuses on various catalyst systems used for this purpose. The activity of catalysts depends on several factors such as the nature of the active metal catalyst and the catalyst support, the precursor used, the method adopted for catalyst preparation, and the presence of promoters as well as reaction conditions like the water-to-ethanol molar ratio, temperature, and space velocity. Among the active metals used to date for hydrogen production from ethanol, promoted-Ni is found to be a suitable choice in terms of the activity of the resulting catalyst. Cu is the most commonly used promoter with nickel-based catalysts to overcome the inactivity of nickel in the water-gas shift reaction. γ-Al₂O₃ support has been preferred by many researchers because of its ability to withstand reaction conditions. However, γ-Al₂O₃, being acidic, possesses the disadvantage of favouring ethanol dehydration to ethylene which is considered to be a source of carbon deposit found on the catalyst. To overcome this difficulty and to obtain the long-term catalyst stability, basic oxide supports such as CeO₂, MgO, La₂O₃, etc. are mixed with alumina which neutralises the acidic sites. Most of the catalysts which can provide higher ethanol conversion and hydrogen selectivity were prepared by a combination of impregnation method and sol-gel method. High temperature and high water-to-ethanol molar ratio are two important factors in increasing the ethanol conversion and hydrogen selectivity, whereas an increase in pressure can adversely affect hydrogen production.     

Optoelectronic and morphology properties of perovskite/silicon interface layer for tandem solar cell application

Silicon (Si) solar cell has low optical absorption because of the low and indirect bandgap of Si, and the efficiency was trapped at 25% for 15 years. Si solar cell is able to achieve efficiency up to 30% by adding perovskite as multiple bandgap material through tandem formation. In this paper, the Si/perovskite interface layer was characterized to study the compatibility of perovskite on fluorine-doped tin oxide (FTO) glass and p-type Si wafer (p-Si). The single solution deposition step of methyl ammonium lead iodide, CH₃NH₃PbI₃ (MAPbI₃) perovskite film, was spin-coated at different concentration. The physical properties of the MAPbI₃/FTO and MAPbI₃/p-Si were obtained by profilometer, atomic force microscope, X-ray diffraction, and Raman spectroscopy. The optical properties were analyzed by ultraviolet-visible spectroscopy, photoluminescence, and infrared transmission. Then the electrical properties were measured by Hall effect. From the measurement, it is observed that 1.2M concentration of MAPbI₃ thin film has the highest thickness, smoothest film surface, and largest crystallite size compared with 0.8M and 1.0M. It is found that there is an interaction in perovskite/Si interface and caused in a low-wavelength shift, and the increase in concentration of MAPbI₃ helped in intensifying the Raman signal produced. 1.2M MAPbI₃ thin film had the highest enhancement in light trapping property rather than 0.8M and 1.0M. The bulk concentration and conductivity of 1.2M perovskite were higher, but the resistivity was lower than 0.8M MAPbI₃ because of more CH₃NH₃I and PbI₂ concentration within MAPbI₃ perovskite compound.     

Radiological hazard analysis of Malaysia’s ceramic materials using generic and RESRAD-BUILD computer code approach

In this study, 52 samples of ceramic materials were studied for ²²⁶Ra, ²²²Rn, ²³²Th and ⁴⁰K natural radionuclides using high-purity germanium detector and relevant radiological hazards parameters were also appraised. Furthermore, the long-term variations of the total effective dose equivalent (TEDE) and effects of wall thickness on TEDE were established and analyzed using RESRAD-BUILD computer code. The observed percentage variations of TEDE are 2% and 8% for ²²⁶Ra and ²³²Th, respectively, while no variation observed for external dose due to ⁴⁰K. The estimated indoor doses from the studied ceramic materials are all below the recommended maximum limit.

     

Estimate of the limitations in data transmission imposed on digitally modulated laser diodes by the bit pattern

In this paper, the cut-off bit-pattern phenomenon of a digitally-modulated semiconductor laser diode (LD) is calculated. The cut-off bit-pattern $\left( {Q_{\textit{off}}^{\textit{cut}\text{- }\textit{off}} }\, \right) $ Q off cut - off is defined as the number of “0” bits (i.e., OFF pulses) preceding the considered “1” bit (i.e., ON pulse) above which an LD cannot respond normally to an injected data pattern and will consequently shutdown or become inoperable. The latter case occurs when the turn-on time delay of an LD exceeds the bit-time interval of the injected current pulse. An analytical calculation for an LD’s cut-off bit-pattern is derived in terms of laser cavity parameters, bit rate, modulation and dc-bias currents. This calculation can be used to predetermine, based on typical values for an LD, accurate dc-bias and modulation current values that should be utilized to ensure an LD is operational for high-speed optical communications applications.     

Smoothing effects on the IMR and ITR

This paper is a study of the effects of smoothing on the implicit midpoint rule (IMR) and the implicit trapezoidal rule (ITR) with implications for extrapolation of the numerical solution of ordinary differential equations. We extend the study of the well-known smoothing formula of Gragg to a two-step smoothing formula and compare the effectiveness of their use with the IMR and ITR for nonstiff and strongly stiff cases. We present an analysis of the Prothero-Robinson problem and as well as experimental results on linear and nonlinear problems.     

Development and implementation of Høgdahl convention and Westcott formalism for k<Subscript>0</Subscript>-INAA application at Malaysian Nuclear Agency reactor

The present work shows the development of k₀-instrumental neutron activation analysis (k₀-INAA) method at the Malaysian Nuclear Agency research reactor. To use the k₀-INAA method, two formalisms were regulated according to 1/ν and non-1/ν (n, γ) reaction nuclides. The reactor neutron spectrum parameters, the thermal to epithermal neutron flux ratio (f), the epithermal neutron flux shape factor (α) were measured using the bare bi-isotopic monitor and bare triple monitor methods, respectively, based on the Høgdahl convention. In addition, the modified spectral index \( r(\alpha )\sqrt {T_{n} /T_{0} } \), the Westcott \( g_{Lu} (T_{n} ) \) factor and the absolute neutron temperature T _n parameters were determined using the Westcott formalism. ¹⁷⁶Lu was used as non- 1/ν monitor while ¹⁹⁷Au, ⁹⁶Zr and ⁹⁴Zr were used as 1/ν monitors. The average values of \( r(\alpha )\sqrt {T_{n} /T_{0} } ,\,g_{Lu} (T_{n} ) \) and T _n were determined to be 0.1795 ± 0.0044, 1.9729 ± 0.0234 and 50.12 ± 3.21°C, respectively. The accuracy of the method was evaluated by analysing IAEA-Soil 7, IAEA-SL 1, NBS SRM 1633A-1 and IAEA-Soil 375 as reference materials. The results show an acceptable level of consistency.