Hybrid routing scheme using imperialist competitive algorithm and RBF neural networks for VANETs

Wireless Networks - Vehicular ad hoc network (VANET), a special type of mobile ad-hoc networks (MANETs), is characterized by a very high mobility. Due to the dynamic nature of vehicle nodes and...     

Post-fire behavior of CFRP retrofitted thin-walled steel tanks

Thin-walled shell structures are characterized by a lightweight structural form with high strength. This structure has many applications in various engineering fields and is considered to be a basic tool in the modern industry. This study investigates the effect of CFRP on tanks after post-fire in order to examine the buckling and post-buckling of the cylindrical tanks. Herein, post-fire was introduced at different temperatures (150°C-600°C). Ten laboratory specimens in two groups with verified temperatures, under external pressure, are examined. The models were designed to demonstrate how repairing steel tanks, which are damaged by fire, by using carbon-fiber-reinforced polymer can recover lost capacity. The results of testing under different theories and codes were compared. This study shows that the initial buckling load of the temperature group increased by 30.82% to 57.09% compared to the temperature without-CFRP group. The overall buckling load of the temperature group increased by 37.01% to 67.74% compared to the temperature without-CFRP group. The collapse load of the temperature group increased by 27.04% to 52.64% compared to the temperature without-CFRP group. And using carbon-fiber-reinforced polymer on models, which are damaged by fire, can be an improvement behavior for the buckling and post-buckling specimen tests.     

Toughening Mechanisms in Cemented Carbides

Plastic zones much larger than previously expected have been observed around cracks in several cemented carbide materials. A preliminary estimate of the crack tip shielding due to the plastic zone in one material suggests that a substantial fraction of the fracture toughness may be due to the zone. Moreover, reduced zone sizes were observed in regions of rapid crack growth, implying that the dynamic fracture toughness may be smaller than the quasi-static value.     

Design of all-optical simultaneous AND,NAND, OR,and NOR logic gates using phase-based control of three coupled waveguides

In this paper, we present a novel phase-based structure for implementing the all-optical multi-function logic gates. The proposed structure which is composed of three coupled waveguides allows us to simultaneously access OR/NOR and AND/NAND logic functions from different output ports. The phase of middle waveguide plays the role of control tool which defines the logical values of outputs. The output ports can be switched from OR/NOR to AND/NAND logic functions by changing the control phase from 24\(^{\circ }\) to 237\(^{\circ }\), respectively. Beam propagation method has been employed in order to accomplish the simulations of light propagation.     

Renewable energy harvesting with the application of nanotechnology: A review

It is believed that fossil fuel sources are exhaustible and also the major cause of greenhouse gas emission. Therefore, it is required to increase the portion of renewable energy sources in supplying the primary energy of the world. In this study, it is focused on application of nanotechnology in exploitation of renewable energy sources and the related technologies such as hydrogen production, solar cell, geothermal, and biofuel. Here, nanotechnologies influence on providing an alternative energy sources, which are environmentally benign, are comprehensively discussed and reviewed. Based on the literature, employing nanotechnology enhances the heat transfer rate in photovoltaic/thermal (PV/T) systems and modifies PV structures, which can improve its performance, making fuel cells much cost‐effective and improving the performance of biofuel industry through utilization of nanocatalysts, manufacturing materials with high durability and lower weight for wind energy industry.     

Combination of baffling technique and high-thermal conductivity fluids to enhance the overall performances of solar channels

In the present study, two-phase flow and forced-convection heat transfer of hydrogen gas (H₂) in a solar finned and baffled channel heat exchanger (SFBCHE) is studied numerically. The effect of different obstacles in the channel is addressed. A H₂ heat transfer fluid (HTF) having a high thermal conductivity with the baffling technique is implemented to enhance the overall performance of a solar channel. In the initial step, the results from the proposed numerical model were compared with the experimental data of a smooth channel, and then against data with a baffled channel. After checking the validity of our model, the same numerical approach was used for studying thermal-fluid characteristics of the channel with the new fluid. A hydrothermal analysis is presented for a range of Reynolds number (Re) from 5000 to 25,000. At the lowest Re = 5000, the thermal enhancement factor (TEF) is about 1.25. This value increases to 2.16, or 73.46%, when Re = 10,000. This increase in the TEF values continues as Re increases. The largest Re = 25,000 gives the highest TEF value, as it is about 4.18, which is 2.75 times greater than that given for the case of using the conventional gaseous fluid (air). Therefore, our proposed structure for the SFBCHE with high H₂ HTF flow velocity leads to improve the values of dynamic pressure (P_d) and heat transfer (Nu), while reducing the skin friction (f) values, which increases the overall TEF of the channel. In addition, all performance values are greater than unity (or 1.00). This reflects the importance of the H₂ HTF baffling and finning technique in improving the hydrodynamic thermal-energy performance of solar heat exchangers. The suggested model of SFBCHE filled with an H₂ HTF having a high thermal conductivity allows a considerable enhancement in the overall thermal performances which can be employed in various thermal types of equipment, such as solar energy receivers, automotive radiators, and cooling in chemical industries.

     

Stability improvement of a dynamic walking system via reversible switching surfaces

Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be reshaped back into its old style, together with the disturbance rejection. (iii) The stabilization procedure has to be performed with as small energy consumption as possible. Because of the reversibility effects of the switching surfaces in the above rules, the terminology of “Reversible Switching Surfaces” (RSS) is employed to address the control scheme; so the control objective would be the implementation of RSS for a bipedal robotic system. In this paper, this aim is achieved by a kinematically controlled foot scheme that is implemented on a simple structured biped. The presented idea is validated by a commercial version of MSC Adams software.     

Alumina Nanopowder Production from Synthetic Bayer Liquor

Alkoxides are the most common precursors used for the production of alumina nanopowders. These materials are, however, expensive and corrosive. This paper introduces a new method for the production of alumina nanopowders by rapid cooling of a synthetic caustic sodium aluminate solution (Bayer liquor), followed by calcination in the presence of a surface-stabilizing agent like 1,2-dihydroxy-3,5-benzene disulfonic acid disodium salt (Tiron). The powders produced are characterized by differential thermal analysis, XRD, transmission electron microscopy, scanning electron microscope, and Brunauer–Emmet–Teller. A nanopowder of α-alumina with an average crystallite size of 27.7 nm and an average particle size of 50 nm is produced.     

Boehmite nanopetals self assembled to form rosette-like nanostructures

Rosette-like boehmite nanostructures were prepared successfully via a simple hydrothermal process. The obtained material was characterized with X-ray powder diffractometry (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Using Scherrer formula, the average crystallite size of the obtained boehmite rosettes was measured to be about 8 nm. It was shown that boehmite nanopetals with average width of about 41 nm determined by TEM, were formed during the hydrothermal process and then self assembled due to weak hydrogen bonds to fabricate boehmite rosettes. The specific surface area of the obtained rosette-like nanostructures was calculated through BET N₂-adsorption technique to be about 143.08 m²/g.     

A Novel 3-D Nanoporous Ce(III) Metal-Organic Framework with Terephthalic Acid; Thermal,Topology, Porosity and Structural Studies

This study describes the synthesis, crystal structure, porosity, and thermal stability of a new three-dimensional nano-porous metal-organic framework, [Ce₂(tp)₃(DMF)₂(DMSO)₂]_n, 1, (H₂tp = terephthalic acid, DMF = dimethyl formamid, DMSO = dimethyl sulfoxide). Compound 1 was synthesized by the solvothermal reaction of Ce(NO₃)₃·6H₂O and H₂tp and was then characterized by single-crystal X-ray diffraction and infrared spectroscopy. Structural analysis of 1 showed that Ce(III) ion has coordination number nine in a distorted mono-capped square anti-prismatic geometry. Gas sorption studies revealed a relatively reversible type-I isotherm characteristic of a porous material with surface area, pore volume, and average pore size of 179.4 m² g^?1, 0.73 cm³ g^?1, and 3.8 Å, respectively.