Orouji A.A.,Semnan UniversitySemnan |
Hanaei M.,Semnan UniversitySemnan
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2015
Abstract In this paper, a novel silicon on insulator (SOI) lateral diffused metal oxide semiconductor (LDMOS) transistor with high voltage and high frequency performance is presented. In this work we try to reduce the electric field crowding in the drift region. The proposed structure consists of a metal in the buried oxide and also connected to the source. The inserted metal attracts the electric field lines in the buried oxide. It causes 67% improvement in the breakdown voltage in comparison with a conventional SOI-LDMOS (C-LDMOS). Our simulations with two dimensional ATLAS simulator show that the gate-drain capacitance improves in the proposed structure. The unilateral power gain also enhances. So, the proposed structure is suitable for high voltage and high frequency applications. © 2015 Elsevier B.V.
Ajami A.,Vienna University of Technology |
Ajami A.,Semnan UniversitySemnan |
Husinsky W.,Vienna University of Technology |
Svecova B.,Institute of Chemical Technology Prague |
And 2 more authors.
Journal of Non-Crystalline Solids | Year: 2015
Abstract The commercially available glass BK7 was chosen to prepare silver-rich layer within the glass by the silver (Ag) ion exchange method in order to enhance its nonlinear optical properties. The glass substrates were doped with Ag at 320°C by a 50-minute Ag+ 虠 Na+ ion exchange in a melt of NaNO3 and KNO3 containing 14 mol% of AgNO3. Then, one piece of glass BK7 containing Ag ions (as-exchanged sample) was annealed in air for 1 h at 600°C to prepare the as-annealed sample. The thickness of the layer containing Ag in the as-exchanged glass BK7 was measured to less than 1 μm. It was found that during the post-exchanged annealing most silver diffused deeply into the glass substrate leading to increase the thickness of the layer to 110 μm. However, some amount of Ag nucleated during the annealing, thus creating small nanoparticles (NPs) with an average size of 2 nm. The linear and nonlinear optical properties of the as-exchanged and as-annealed glass BK7 were studied. The as-exchanged sample showed no absorption in the visible spectral region whereas, as-annealed glass BK7 showed a peak absorption at 420 nm which can be attributed to the presence of Ag NPs formed in this glass. The nonlinear optical behavior of the samples was investigated using 800 nm and 400 nm femtosecond pulses. Strong saturable absorption was observed in the as-annealed sample at 400 nm. This feature promises an efficient way for designing all optical switching devices appropriate for the second harmonic of the Ti-sapphire laser. Using nonlinear transmission (NLT) method the saturation intensity for the as-annealed sample was determined 8.5 × 1011 W·cm- 2. An intensity dependent switching from saturable absorption (SA) to reverse saturable absorption (RSA) was also observed when the as-annealed sample was irradiated simultaneously by 800 nm and 400 nm femtosecond pulses. © 2015 Elsevier B.V.
Shafabakhsh G.H.,Semnan UniversitySemnan |
Faramarzi M.,Guilan University |
Sadeghnejad M.,Islamic Azad University at Tehran
Construction and Building Materials | Year: 2015
Aggregate-asphalt binder adhesion bond is a vital factor that affects the resistance of asphalt mixtures against moisture damages. Since, moisture damages are the main defects of sulfur extended asphalts (SEAs), this study aims to improve it by reinforcing the adhesion between asphalt binder and aggregate. An antistripping additive named nanotechnology Zycotherm (NZ) was used to achieve this goal. Surface Free Energy (SFE) method was applied to examine the effectiveness of NZ additive in improving the moisture susceptibility of SEA. The research team utilized two common mechanical tests (indirect tensile strength, and dynamic modulus) to evaluate the validation of SFE method. All samples were constructed with two different aggregates, limestone and granite. In the SFE method, the measured surface energy components of constitutive materials were used to calculate the bond strength between them in dry and wet conditions. The findings showed that adding NZ was a successful technique to compensate the deteriorated adhesion due to using sulfur. Also it was demonstrated that SFE test results were so compatible with the common mechanical tests in predicting moisture damages. © 2015 Elsevier Ltd. All rights reserved.
Darzi S.,National University of Malaysia |
Sieh Kiong T.,University of Tenaga Nasional |
Tariqul Islam M.,National University of Malaysia |
Rezai Soleymanpour H.,Semnan UniversitySemnan |
Kibria S.,National University of Malaysia
Applied Soft Computing Journal | Year: 2016
This paper introduces a memory-based version of gravitational search algorithm (MBGSA) to improve the beamforming performance by preventing loss of optimal trajectory. The conventional gravitational search algorithm (GSA) is a memory-less heuristic optimization algorithm based on Newton's laws of gravitation. Therefore, the positions of agents only depend on the optimal solutions of previous iteration. In GSA, there is always a chance to lose optimal trajectory because of not utilizing the best solution from previous iterations of the optimization process. This drawback reduces the performance of GSA when dealing with complicated optimization problems. However, the MBGSA uses the overall best solution of the agents from previous iterations in the calculation of agents’ positions. Consequently, the agents try to improve their positions by always searching around overall best solutions. The performance of the MBGSA is evaluated by solving fourteen standard benchmark optimization problems and the results are compared with GSA and modified GSA (MGSA). It is also applied to adaptive beamforming problems to improve the weight vectors computed by Minimum Variance Distortionless Response (MVDR) algorithm as a real world optimization problem. The proposed algorithm demonstrates high performance of convergence compared to GSA and Particle Swarm Optimization (PSO). © 2016 Elsevier B.V.
Golestanbagh M.,Semnan UniversitySemnan |
Parvini M.,Semnan UniversitySemnan |
Pendashteh A.,Guilan University
Energy Sources, Part A: Recovery, Utilization and Environmental Effects | Year: 2016
Produced water (PW) is considered as one of the largest waste streams in the petroleum, oil, and gas industry. The drilling and extraction operations aiming to maximize the production of oil may be counterbalanced by the huge production of contaminated water with pollutants, such as heavy metals and organic compounds. This review provides insight into the implementation of different technologies in the petroleum industry for treating PW generated from conventional oilfields in upstream and downstream processes. Scientific efforts in the future can concentrate on developing the most economical and environmentally compliant solutions for the management of untreated PW. © 2016 Taylor & Francis Group, LLC.
Davoodi A.,Semnan UniversitySemnan |
Tajally M.,Semnan UniversitySemnan |
Mirzaee O.,Semnan UniversitySemnan |
Eshaghi A.,Iran University of Science and Technology
Optik | Year: 2016
Utilizing the sol–gel method, Al-Ti codoped ZnO (ATZO) thin films were deposited on glass substrates. The effects of annealing at different temperatures (500, 550 and 600 °C) and post annealing in reducing atmosphere on the structure, optical and electrical properties of the ATZO thin film were studied. The X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) methods were used to investigate the structure, morphology and surface roughness of the thin films. The optical properties were investigated by UV–vis spectrophotometer. The XRD results show that increase in annealing temperature from 500 to 600 °C lead to increase in grain size from 19 to 31 nm. The obtained results of the XRD analysis were confirmed by the FE-SEM morphological characterization. The AFM measurements exhibit that the RMS roughness varies between 6.9–10.3 nm. It was concluded that the increase in the annealing temperature of the thin films up to 550 °C lead to improvement in the transparency and reduction of the resistivity. It was revealed that post annealing in a reducing atmosphere of 95% N2–5% H2 caused a significant reduction of the resistivity along with an increase in transmittance. © 2016 Elsevier GmbH
Zolfaghari A.A.,Semnan UniversitySemnan |
Taghizadeh-Mehrjardi R.,Islamic Azad University at Ardakan |
Asadzadeh F.,Urmia University |
Hajabbasi M.-A.,Isfahan University of Technology
Archives of Agronomy and Soil Science | Year: 2016
In this study, the effect of land-use treatments and the feasibility of fractal dimension to quantify soil aggregate stability were investigated in the central Zagrous, Iran. For this purpose, the non-linear fractal dimension (Dnl), linear fractal dimension (Dl) and the mean weight diameter (MWD) of aggregates were compared. Soil samples from three sites with four adjacent land-use types, namely: forest area (F), cultivated lands adjacent to forest (CAF), pasture (P) and cultivated lands adjacent to pasture (CAP) were collected. Results showed that soils under cultivated lands had higher bulk density (BD) (1.30–1.38 Mg m−3) compared to the adjacent soils under forest (1.19 Mg m−3) and pasture (1.21 Mg m−3). In the 0–15 cm layer, soil organic matter (SOM) content in the cultivated plots were respectively 30% and 31% lower compared to the forest and pasture soils. The lowest CVs belonged to Dnl (5–8%) demonstrating that Dnl was more accurate than Dl (8–14%) and MWD (30–53%) methods. CAP had the largest value of Dnl, while P had the smallest value of Dnl. Difference of Dnl between forest and pasture was not significant, whereas both of them significantly differed from CAF and CAP. Dl did not differ significantly between forest and CAF. There were significant differences between forest and pasture for the measured MWD. Both fractal dimensions had negative correlation with MWD, SOM, hydraulic conductivity (HC) and macroaggregates (>0.25 mm) and positive correlation with BD and total porosity (TP). © 2015 Taylor & Francis.