Sharif Digital Repository

In this work, a new structure of single layer armchair graphene nanoribbon field effect transistor with the Stone–Wales (SW) defect (SWGNRFET) is studied. The simulations are solved with Poisson–Schrödinger equation self-consistently by using Non-Equilibrium Green Function (NEGF) and in the real space approach. The energy band structure is obtained by approximation tight-binding method. The results show that displacement of a defect in the width of the channel of the new structure is led to 50% increase in ION/IOFF ratio only by rotating of a C–C (Carbon–Carbon) bond with similar behavior. But, a remarkable increase of 300% in ION/IOFF ratio is obtained by a “dual center” defect. The results... 

Our aim is to improve the switching performance of the graphene nanoribbon field-effect transistors (GNRFETs), exploiting the concept of energy filtering. Within the proposed scheme, a superlattice (SL) structure is used in the source of the transistor for filtering high-energy electron tail by engineering the density of states (DOS). According to simulation results, this can significantly decrease the OFF-current and the subthreshold swing (SS). A comparison of the proposed device with a conventional GNRFET and a graphene nanoribbon (GNR) tunneling field-effect transistor (GNRTFET) demonstrates a significant improvement. Therefore, a typical SL-GNRFET can reduce the average and the minimum... 

We are proposing a next-generation graphene nanoribbon field-effect transistor (GNRFET) with superlattice source, channel, and drain (SLSCD-GNRFET), with significantly improved switching performance. The presence of superlattice in each region is for energy filtering. The simulation results indicate that the addition of an appropriate superlattice in the channel region, it reduces the subthreshold swing. Also, using proper superlattice in the drain region leads to an increase of more than a decade in the ION/IOFF ratio by intensely reducing the OFF-current. These improvements make the proposed transistor potentially suitable for the next-generation logical digital applications. Comparison of... 

In this paper, a method of determining physical dimension of Double Barrier Quantum Well (DBQW) of Resonance Tunneling Diodes (RTDs) is presented by using I-V characteristic governing on them. In this procedure, first we have used performance metrics related to RTDs I-V characteristic such as Peak to Valley Current Ratio (PVCR), peak current density (JP), valley current density (JV) and Voltage Swing (VS), and by some other arbitrary points, we have fitted a curve to the RTD current-voltage equation by MATLAB software. Then we have obtained the physical parameter of I-V equation and adjusted some of them with modification coefficients. Next, by choosing the material of barriers and the well... 

A new non-enzymatic sensor for glucose is prepared by using of Ni(II)-one dimensional coordination polymer (Ni(II)-Cp) and C 60 . The Ni(II)-Cp prepared by slow diffusion and evaporation of two solution layers of NiCl 2 and diaza-macrocycle bearing two pyridine side arms (as the reported tecton) in DMF. The Ni(II)-Cp was characterized by powder x-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as Fourier transform infrared spectroscopy (FT-IR). C 60 as modified was added to Ni(II)-Cp for improving the electrical and chemical stability of the composite. The newly assembled Ni(II)-Cp/C 60 also coated on glassy carbon electrode (GC) to... 

We propose a triple-tunnel junction single electron transistor (TTJ-SET). The proposed structure consists of a metallic quantum-dot island that is capacitive coupled to a gate contact and surrounded by three tunnel junctions. To the best of our knowledge, this is the first instance of introducing this new structure that is suitable for both digital and analog applications. I-V D characteristics of the proposed TTJ-SET, simulated by a HSPICE macro model for various gate voltages, are in excellent agreement with those obtained by SIMON, which is a Monte-Carlo based simulator. We show how one can design a digital inverter by using a single TTJ-SET. We also show that, under suitable conditions,... 

Design models of axial flow compressor are developed for high temperature power plants with Closed Brayton Cycle for energy conversion. in recent years, many efforts have been done for modeling and predicting of performance of these compressors on different conditions of speed and pressure ratio because of costly empirical experiments, and still are developing. The models are based on a mean-line through-flow analysis for free-vortex flow, account for the profile, secondary, end wall and tip clearance losses in the cascades. In this work, models of Lieblein, Koch-Smith, Herrig, Johnsen-Bullock, Pollard-Gostelow, Aungier, Hunter-Cumpsty, Reneau are implemented to consider single stage... 

A novel intelligent semi-active control system for an eleven degrees of freedom passenger car's suspension system using magnetorheological (MR) damper with neuro-fuzzy (NF) control strategy to enhance desired suspension performance is proposed. In comparison with earlier studies, an improvement in problem modeling is made. The proposed method consists of two parts: a fuzzy control strategy to establish an efficient controller to improve ride comfort and road handling (RCH) and an inverse mapping model to estimate the force needed for a semi-active damper. The fuzzy logic rules are extracted based on Sugeno inference engine. The inverse mapping model is based on an artificial neural network... 

Using CNG as an additive for gasoline is a proper choice due to higher octane number of CNG enriched gasoline with respect to that of gasoline. As a result, it is possible to use gasoline with lower octane number in the engine. This would also mean the increase of compression ratio in SI engines resulting in higher performance and lower gasoline consumption. Over the years, the use of simulation codes to model the thermodynamic cycle of an internal combustion engine have developed tools for more efficient engine designs and fuel combustion. In this study, a thermodynamic cycle simulation of a conventional four-stroke spark-ignition engine has been developed. The model is used to study the... 

With the declining energy resources and increase of pollutant emissions, a great deal of efforts has been focused on the development of alternatives for fossil fuels. One of the promising alternative fuels to gasoline in the internal combustion engine is natural gas [1-5]. The application of natural gas in current internal combustion engines is realistic due to its many benefits. The higher thermal efficiency due to the higher octane value and lower exhaust emissions including CO2 as a result of the lower carbon to hydrogen ratio of the fuel are the two important feature of using CNG as an alternative fuel. It is well known that computer simulation codes are valuable economically as a cost... 

Gaining insight into possible vibratory responses of dynamical systems around their stable equilibria is an essential step, which must be taken before their design and application. The results of such a study can significantly help prevent instability in closed-loop stabilized systems by avoiding the excitation of the system in the neighborhood of its resonance. This paper investigates nonlinear oscillations of a rotary inverted pendulum (RIP) with a full-state feedback controller. Lagrange’s equations are employed to derive an accurate 2-DoF mathematical model, whose parameter values are extracted by both the measurement and 3D modeling of the real system components. Although the governing... 

A suction-controlled ring device has been developed to continuously measure the coefficient of lateral soil pressure in deformable unsaturated soil samples from the at-rest to the active condition under application of increasing vertical pressure and controlled matric suction. The device incorporates a thin aluminum specimen ring equipped with horizontal strain gages for recording the lateral soil strains. In addition, a sensor recording water volume changes is utilized to continuously monitor the degree of saturation of the soil sample during tests. The matric suction within the soil texture is controlled using the axis translation technique. In order to verify the performance of the ring... 

We introduce a new smooth, non-toxic, biocompatible method for cross-linking of gum tragacanth (GT), a polysaccharide of natural origin, in order to serve as a new supporting matrix for immobilization systems. The modified gum is used as a matrix for the catalysis of the conversion of benzyl penicillin to 6-aminopenicillanic acid (6-APA) by means of Escherichia coli ATCC11105 with penicillin G acylase (PGA) activity. The results show that GT beads can not only serve as a proper matrix for immobilization, but show enhanced hydrolysis rate and stability compared to other immobilization systems used for this reaction. This signifies the potential of GT as a biocompatible matrix for... 

The Class-E power amplifier has been widely studied and formulated in the literature. Although the majority of reported inductive coupling wireless power transfer (WPT) systems use a class-E power amplifier for driving the primary coil, still there is a lack of a comprehensive study on class-E circuit dedicated to WPT, providing a set of closed form design equations for proper class-E operation. This paper presents the required design equations needed to design a 'true' class-E circuit for WPT applications. Equations for the series-tuned secondary coil WPT system are presented, as well as two different design procedures for the parallel-tuned secondary coil. The derived equations have been... 

Pole Side Impact Tes is one out of three crash tests described by Euro NCAP standard for star rating of a vehicle and is required for assessing the Adult Occupant Protection. In this paper the goal is to determine the crashworthiness of side doors and B pillar in a Pole Side Impact Test based on Euro New Car Assessment Program (Euro-NCAP) using computer and simulation method. In this matter, a vehicle model has been prepared and meshed using Hypermesh and CATIA. The velocity of 29 km/h has been assigned to the vehicle which was on top of a cart while the pole has been assigned as a rigid static object based on Euro NCAP requirements specifically. Results show that different amounts of energy... 

To assess a car under the Euro New Car Assessment Program (Euro-NCAP), Adult Occupant Protection is one out of three parameters which need to be calculated with a weight factor of 50% while the other parameters, Child Occupant Protection and Pedestrian Occupant Protection, have a weight factor of 20%. The Pole Side Impact Test, beside two other tests, Side and Front Impact, is also required to calculate the Adult Occupant Protection. It shows how important the Pole Side Impact Test is and what an effective role it has in the car rating assessment. In this paper, the objective is to evaluate the effect of thickness on the energy absorbed by the side doors and the B pillar and its... 

In Euro NCAP standard, adult protection is one of the most important rating scores with 50% weight factor while child protection and pedestrian protection are accounted into consideration with 20% weight factor. For adult protection testing, three tests are required to perform: (1) side impact, (2) pole impact, (3) front impact. In the side impact test, dummy's head, chest, shoulder, thorax, ribs, abdomen, pelvic and femur must be studied to evaluate the rating score. Crashworthiness of a car during side impact can describe the score rated for that car. In this paper the goal is to determine the crashworthiness of side doors and B-pillar in side impact crash est by simulation using LS DYNA... 

In side impact test which is one out of three tests of Euro NCAP standard, front and rear doors and B pillar are most absorbance parts among vehicle body parts. Passengers are highly in danger while side crash, because of the distance between passenger's head and vehicle body. In this paper effect of material and thickness of doors and B-pillar and their absorbed energy during crash and improvement of its crashworthiness with respect to light weight design are studied using LS DYNA solver. The objective of this paper is to propose a material for doors and B-pillar with a specified thickness to achieve maximum absorbed energy and minimum weight. The shape of the doors and B-pillar remains... 

In this study, the influence of CO2 and CH4 on the performance and selectivity of Co-Ru/Al2O3 catalyst is investigated by injection of these gases (0-20 vol.% of feed) to the feed stream. The effect of temperature and feed flow rate are also inspected. The results show that low amounts of CO2 in the feed stream do not change the catalyst activity, but increasing the amount of CO2 (more than 10 vol.%), causes the CO conversion to decrease and the selectivity of heavy components to increase. Methane acts as an inert gas and does not affect the catalyst performance. Increasing feed flow rate has a negative effect on both CO conversion and heavy component selectivity. By raising the temperature,...