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Tehrān, Iran

Abdali M.,Islamic Azad University at Tehran | Mirzakuchaki S.,IUST
Materials Science in Semiconductor Processing | Year: 2014

Recent advances in etching agents and techniques on the fabrication of double-walled carbon nanotubes (DWCNTs) have introduced various techniques and devices based on nanotube technology. The present study evaluates the inter-shell interaction of DWCNT through density functional theory (DFT) and charge transfer model. The results showed that the band structure of a DWCNT is determined by super positioning of the band structures of the two individual CNT constituting the DWCNT. In next step, interwall conductance the electronic properties of DWCNT were studied through the band-structure approach. Our assessments have shown that at lower potentials the amount of intershell leakage current is negligible. © 2013 Elsevier Ltd. All rights reserved. Source

Mearaji F.,Islamic Azad University at Tehran | Tamizifar M.,IUST
International Journal of Refractory Metals and Hard Materials | Year: 2014

In this study, AlN whiskers were prepared in a tube furnace at 1000 °C for 1 h under 500 cc/min nitrogen gas flow. Al powders with particle sizes of 3 μm and 45 μm and NH4Cl were used as raw materials. SEM, TEM and XRD analyses were applied to characterize AlN whiskers. The diameters of AlN whiskers were from 140 nm to 340 nm by using different amounts of NH 4Cl and 3 μm Al powder. In the case of using NH4Cl more than 40 wt.%, pure AlN without any unreacted Al was formed as final product. Using NH4Cl and Al powder with a particle size of 45 μm leads to obtain AlN whiskers with 630 nm to 870 nm in diameter. By adding 50 wt.% NH 4Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing the NH4Cl content in starting materials (about 200 nm). Also increase in diameter of AlN whisker was resulted by using coarse Al powder. By adding NH4Cl to Al, thermodynamically spontaneous chlorination-nitridation reactions in vapor phase were increased and whiskers and pure AlN powder were produced. It seems that the formation of whiskers in this work was related to solid-gas (VS) mechanisms. © 2014 Elsevier Ltd. Source

Shafia M.A.,Iran University of Science and Technology | Rabadi N.J.,University of Jordan | Babakhan A.R.,IUST
International Journal of Manufacturing Technology and Management | Year: 2015

In recent years, technology has played a significant role in the development of many countries and in the creation of wealth for individuals as well as corporations. Literature shows that, in normal conditions, several factors influence the acquisition, the implementation and the success of a certain technology. Those factors may differ depending on the country acquiring the technology or the acquired technology itself. Understanding the optimum match between a country or an industrial firm operating in that country and a particular technology is very useful for investment decisions. This paper presents the factors that influence the selection of an appropriate technology acquisition channel. To illustrate this process a case study of Iranian small and medium die-making industries is investigated using the grounded theory. The data used in the analysis is collected through in-depth interviews with many S&M Iranian industries. The results of the investigation indicate that there are new factors that have not been mentioned before in the literature. Furthermore, the complex interrelationships between those factors are outlined. The proposed model has been validated by those who participated in the interviews and the experts consulted herewith. Copyright © 2015 Inderscience Enterprises Ltd. Source

Akhoon M.S.,IUST | Alamoud A.M.,King Saud University
Superlattices and Microstructures | Year: 2016

In this paper, we propose new structures of lateral bipolar junction transistor (LBJT) on silicon on insulator (SOI) with improved performance. The proposed devices are lateral bipolar transistors with multi doping zone collector drift region and a thick buried oxide under the collector region. Calibrated simulation studies have revealed that the proposed devices have higher breakdown voltage than the conventional device, that too at higher drift doping concentration. This has resulted in improved tradeoff between the on-resistance and the breakdown voltage of the proposed devices. It has been observed that the proposed device with two collector drift doping zones and a buried oxide thick step results in ∼190% increase in the breakdown voltage than the conventional device. The further increase in the number of collector drift doping zones from two to three has increased the breakdown voltage by 260% than the conventional one. On comparing the proposed devices with the buried oxide double step devices, it has been found that an increase of ∼15-19% in the breakdown voltage is observed in the proposed devices even at higher drift doping concentrations. The use of higher drift doping concentration reduces the on-resistance of the proposed device and thus improves the tradeoff between the breakdown voltage and the on-resistance of the proposed device in comparison to buried oxide double step devices. Further, the use of step doping in the collector drift region has resulted in the reduction of kink effect in the proposed device. Using the mixed mode simulations, the proposed devices have been tested at the circuit level, by designing and simulating inverting amplifiers employing the proposed devices. Both DC and AC analyses of the inverting amplifiers have shown that the proposed devices work well at the circuit level. It has been observed that there is a slight increase in ON delay in the proposed device; however, the OFF delay is more or less same as that of the conventional device. © 2015 Elsevier Ltd. All rights reserved. Source

Karimyan P.,Amirkabir University of Technology | Gharehpetian G.B.,Amirkabir University of Technology | Abedi M.,Amirkabir University of Technology | Gavili A.,IUST
International Journal of Electrical Power and Energy Systems | Year: 2014

This paper proposes a new long term scheduling for optimal allocation and sizing of different types of Distributed Generation (DG) units in the distribution networks in order to minimize power losses. The optimization process is implemented by continuously changing the load of the system in the planning time horizon. In order to make the analysis more practical, the loads are linearly changed in small steps of 1% from 50% to 150% of the actual value. In each load step, the optimal size and location for different types of DG units are evaluated. The proposed approach will help the distribution network operators (DNOs) to have a long term planning for the optimal management of DG units and reach the maximum efficiency. On the other hand, since the optimization process is implemented for the entire time period, the short term scheduling is also possible. The proposed method is applied to IEEE 33-bus test system using both the analytical approach and particle swarm optimization (PSO) algorithm. The simulation results show the effectiveness and acceptable performance of the proposed method. © 2013 Elsevier Ltd. All rights reserved. Source

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