Combination of Mechanical and Electromagnetic Stirring to Distribute Nano-Sized Al2O3 Particles in Magnesium Matrix Composite

Powder Metallurgy and Metal Ceramics - In this article, a novel stirring method has been developed for producing metal matrix nanocomposites, in which two different stirring methods, i.e....     

Optimization of design parameters for nanofluids flowing inside helical coils

In this study water/Al₂O₃nanofluid is used in helical tubes. Copper helical tubes are in constant wall temperature and the fluid flow is laminar. Thermophysical properties of Nanofluids are assumed to depend on particles volume fraction and temperature. To analyze the heat transfer rate and pressure drop in helical coils, Nusselt number, friction factor and thermal–hydraulic parameter are used. Numerical simulation and Taguchi method are used to investigate the effect of fluid flow and geometrical parameters on JF factor. After simulations, Taguchi method is used for finding the optimum condition for the desired parameters. Proposed optimum conditions are simulated to insure the obtained results. Results indicate that Nanofluids improve the thermal–hydraulic performance of helical tubes. On the other hand using Nanofluids don't change the optimized shape factors but temperature dependent properties alter the optimum particle volume fraction.     

Linearity analysis in pipeline A/D converters

A method for estimating integral nonlinearity (INL) in pipeline analog‐to‐digital converters is presented. In this method, errors in each stage are modeled by an equivalent input‐referred gain error and an input‐referred nonlinearity. For a switched capacitor implementation, the proposed model predicts the maximum statistical INL in terms of capacitor mismatch and also provides an exact formula for INL in terms of finite gain of operational amplifiers. Using this model, it is proved that a high per‐stage resolution reduces the power consumption in low‐speed converters, whereas in high‐speed circuits 1.5‐bit or 2.5‐bit stage is more advantageous. It is also shown that when voltage swing is below 1 V, the lower limit for the size of the capacitors is mainly determined by thermal noise rather than by INL. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of wall proximity on forced convection in a plane channel with a built-in triangular cylinder

A numerical investigation has been carried out to analyze the effect of wall proximity of a triangular cylinder on the heat transfer and flow field in a horizontal channel. Computations have been carried out for Reynolds numbers (based on triangle width) range of 100–450 and gap widths (a/h) 0.5, 0.75 and 1. Results are presented in the form of instantaneous contours of temperature, vorticity, with some characteristics of fluid flow and heat transfer; such as time-averaged and instantaneous local Nusselt number, skin friction coefficient along bottom channel's wall, and drag coefficient. Results show that approaching triangular cylinder in the wall, removes vortex shedding and subsequently the heat transfer rate decreases at low Reynolds number. By decreasing the vortex shedding, drag coefficient decrease as triangular cylinder approaches the wall of the channel. The variation of vortex formation has a more significant suppression effect on the skin friction coefficient than the Nusselt number.     

Kuy-e Narmak (1952–1958): the growth and change of an urban community in Tehran

ABSTRACT

This article examines the growth and change through time of Kuy-e Narmak, a housing neighbourhood developed in the 1950s under the auspices of Mosaddeq’s Modernization Program. The project was designed by a group of young-leading European-educated Iranian architects that collaborated with the government to develop affordable housing solutions in Iran. To design this project, these architects advanced solutions that explored a cross-pollination between the principles of the functional city, and references from vernacular architecture. Over the last 6 decades, the number of households living in Narmak increased dramatically, from the initial goal of accommodating 7500 families, to the 90,000 families that currently live there. This article discusses the extent to which the initial design decisions were instrumental to cope with this extraordinary increase in the district’s density. We have used typological and morphological analysis, combined with site surveys and interviews to investigate the district’s growth and change through time. This article argues that the designer’s critical combination of modernist planning concepts with elements borrowed from Iran’s vernacular tradition resulted in a socially inclusive urban community. The plan’s rigid urban form has become instrumental in defining a neutral background to accommodate the ever-changing social and spatial practices of its inhabitants.     

An adaptive CSMA/TDMA hybrid MAC for energy and throughput improvement of wireless sensor networks

IEEE 802.15.4 as a standard for low rate wireless personal area networks (LR-WPAN) is an applicative choice for implementation of wireless sensor networks. Due to the advantages of this standard and its capabilities for more specification to wireless sensor networks, we were persuaded to resolve some of its proven weaknesses in such environments. The slotted CSMA/CA method utilized in beacon-enabled mode of 802.15.4 causes unacceptable level of energy consumption and throughput in conditions like high loads. To overcome these issues, we proposed an adaptable CSMA/TDMA hybrid channel access method by applying some modifications to the 802.15.4 standard. The energy and throughput improvement is achieved by dedicating a part of the contention access period to a time division medium access protocol (TDMA). To evaluate our proposed method in comparison with 802.15.4, we developed a simulation in OMNeT++. Analysis of the simulation results indicates general improvement of energy consumption and throughput. As a sensor network grows more populated or the load increases, the proposed method shows a better performance in comparison with IEEE 802.15.4 standard.     

Experimental study and optimization of heavy liquid hydrocarbon thermal cracking to light olefins by response surface methodology

Response surface methodology coupled with central composite design (CCD) was used to investigate the effects of operating variables, namely, coil outlet temperature (COT), flow rate and steam ratio, on the yield of light olefins (ethylene and propylene) in thermal cracking of heavy liquid hydrocarbon. From the CCD studies the effects of COT and flow rate were concluded to be the key factors influencing the yield of light olefins. Based on this experimental design, two empirical models, representing the dependence of ethylene and propylene yields on operating conditions, were developed. The single maximum response of ethylene and propylene yields and simultaneous maximization of both responses have also been obtained at the corresponding optimal independent variables. The results of the multi-response optimization could be used to find the suitable operating conditions.