Abstract: The steady, nonsimilar MHD boundary layer flow over a moving cylindrical rod has been investigated. The nonlinear coupled partial differential equations governing the flow have been solved numerically using the Kellar box method. The results indicate that the magnetic field enhances the skin friction coefficient, while it reduces the velocity profile.
Abstract: Electromagnetic compatibility is achieved by reducing the interference below the level that disrupts the proper operation of the electronic system or subsystem. This compatibility is generally accomplished by means of electronic filters, and component or equipment shielding. Shielding an electromagnetic field is a complex and sometimes formidable task. The reasons are many, since the effectiveness of any strategy or technique aimed at the reduction of the electromagnetic field levels in a prescribed region depends largely upon the source (s) characteristics, the shield topology, and materials. In this paper, the effect of an incident plane wave with linear polarization on aluminum shield in UHF frequency is investigated, then, the type of shield material is changed and shielding effectiveness caused by it is investigated. Also, the linear polarization of incident wave is converted to circular polarization and shielding effectiveness variation is obtained in this stage. Slots and apertures are very important parameters to determine suitable shielding effectiveness. In following paper, slot is placed on shield, and its shielding effectiveness is evaluated. The effects of slot width variation, slot length variation and slot displacement, on shielding effectiveness are investigated. Finally, the effect of different aperture structure is evaluated and shielding factor is obtained in any stage. The whole of simulations in this paper, are done with CADFEKO.
Abstract: Paper unavailable due to copyright issues.
Abstract: In this paper, we used the Imperialist Competitive Algorithm (ICA) and Genetic Algorithm (GA) to find the minimum weight design of torispherical dome ends under external pressure load. According to fabrication and strength of material requirements, a group of compromised counters are selected and studied. Based on ASME Section VIII and BS5500 pressure vessel codes, a reasonable buckling pressure limit is proposed. Four-centered ellipse method is quite effective in designing and constructing the dome structure and it is used here to construct the torispherical dome ends. Two different size torispherical dome end models are selected and studied. Imperialist competitive algorithm is found to be very efficient and easy to use for the applications.
Abstract: The main purpose of this research is to propose and develop energy saving inverter controlled magnetic jack. It is an electromechanical load lifting machine which provides controlled linear motion to the load. The project is carried out as a result of increase demand for limited fossil energy. Energy saving of the system is achieved through the use of power electronic inverter connected to the induction motor with sensors installed in some part of the system. The regenerative energy of the system achieved through repulsion of the magnets and increase in thickness of the system coil housing is either saved in the system capacitor which could be re-used later or fed back to the mains. Results show that the system is efficient in energy saving and regeneration. A total of 35.99% energy is expected to be realized by the system at the end of the work. The work is also expected to open new door for researchers in this field.
Abstract: Micro-strip line is a kind of transmission line that is the most widely used in microwave integrated circuit. With the development of microwave integrated circuits and the increasing work frequency of the micro-strip line, a higher requirement for its electromagnetic compatibility has been raised. Finite-Difference Time-Domain (FDTD) method has characteristics of good adaptability in the analysis of electromagnetic compatibility issues and superiority in complexity of the structure modeling. For these reasons, this Article uses FDTD method which is widely used in electromagnetic field calculation to analyze the time-domain of micro-strip line, calculates its current and voltage induced in ports and discuss the response feature under different radiation conditions.
Abstract: Thermal contact resistance plays an important role in many domains, such as microelectronics and nuclear reactors. This paper proposes a more comprehensive model for the prediction of constriction resistance of rough contact between nominally flat surfaces in vacuum. Firstly, a 3D geometrical asperity contact model is proposed based on the analysis of the profile of actual engineering surface. In this model, the contact is not simplified as a rough surface contacting with a perfectly smooth surface, but described as two rough surfaces. Oblique contact is considered and the effects of several parameters such as the shape of the asperity, the depth of interference, and the radial distance between the centerlines of the contacting asperities are investigated. Some mathematical derivations for constriction resistance are performed, and a series of numerical simulations are also carried out, covering a wide range of values of these parameters in practice applications. A comprehensive correlation for constriction resistance as a function of these parameters is finally obtained by nonlinear curve fitting, and it is validated through some comparisons and it can be used to predict more accurately the thermal contact resistance between rough surfaces.
Abstract: An InN film was grown on sapphire (c-plane) by plasma-assisted molecular beam epitaxy, and its photoluminescence at 10 K and photoreflectance (PR) spectra from 10 K to 110 K were measured. Some prominent features in the PR spectra were observed in the infrared region below 120 K. The signals become too weak to observable for temperature above 110K. Furthermore, the binding energy of InN exciton was estimated to be 9.43 meV, which is equal to kBT at 109K. Therefore, the features in the PR spectra were assigned to the A, B, and C excitonic transitions associated with the direct gap of wurtzite InN. The thus obtained energies of the A, B, and C excitonic transitions versus temperature were fitted well by Varshini’s equation. The energies of the A, B, and C excitonic transitions at room temperature obtained by the best fit of Varshni’s equation are 0.738, 0.746, and 0.764 eV, respectively.
Abstract: A high-quality crack-free AlN cap layer on GaN layer has been achieved using an AlN buffer layer directly grown on a silicon substrate at high temperature by radio frequency (RF) plasma-assisted molecular beam epitaxy. A two dimensional (2D) growth process guide to AlN cap layer of high grade crystal quality. The nucleation and the growth dynamics have been studied by in situ reflection high energy electron diffraction (RHEED) and ex situ by high resolution transmission electron microscopy (HR-TEM). The microstructure was investigated by energy-dispersive X-ray spectroscopy (EDX). It was disclosed that AlN is single crystalline with low defect. High densities of V-shaped pits were not detected at the interface between AlN and GaN layers. Contradictory the earlier reported V-shaped defects in nitride-based alloys; these V-shaped pits were condensed on top of the AlN layer because of H2 etching of the surface when a high temperature growth discontinuity between AlN and GaN layers.
Abstract: NH4Al (OH) 2CO3 (AACH) hollow spheres and solid spheres were successfully synthesized with water in oil in water (W/O/W) emulsion, applying the liquid-to-liquid-phase boundary of the micellar system as a template. During the facile procedure, no high pressure, high temperature, or other complex reaction conditions were required. Transmission electric microscope (TEM) images showed that all the hollow structural products have a good spherical morphology with an average diameter of 1 μm. The as-synthesized spheres had large diameters and thin shells of about 30 nm composed of numerous small nanocrystals. In addition, the AACH product can be calcined into Al2O3 without changing its shape.