فهرست مطالب

  • Volume:31 Issue: 5, 2018
  • تاریخ انتشار: 1397/03/05
  • تعداد عناوین: 22
  • A. Alavi Gharahbagh, F. Yaghmaee Pages 684-692
    Abstract Based on rapid upsurge in the demand and usage of electronic media devices such as tablets, smart phones, laptops, personal computers, etc. and its different display specifications including the size and shapes, image retargeting became one of the key components of communication technology and internet. The existing techniques in image resizing cannot save the most valuable information of images on display devices with different resolutions. Seam carving is a standard technique for content-aware resizing of images and videos with negligible distortion. However, seam carving resize high-resolution videos and high quality images with high computational complexity; this limits its real-time applications. In this paper, we present a novel approach to reduce seam carving process time. In the proposed technique, the image was split into three equal parts: upper-middle-lower (or right-middle-left) using horizontal or vertical strips. The middle strip was analyzed by original seam carving technique. For other strips (upper-lower), the seam was obtained employing Dijkstra fixed start point technique. In our proposed technique, unlimited Dijkstra depth search was replaced with a limited depth search. It enhances the computational efficiency of Dijkstra technique for the upper and lower strips. The experimental results showed much better computational efficiency than the current enhanced seam carving techniques. These results indicate that computational complexity is superior, while still maintaining the output quality of the original seam carving method.
    Keywords: Seam Carving, Image Resizing, Image Retargeting, Dijkstra Method, Strip Partitioning
  • K. Shahzad, M. Bilal Khan Pages 693-698
    In this paper we present a system that could be used to help people with walking disabilities. A system consists of a prototype mobile robot platform equipped with a control board and a remote computer system, running with image processing algorithms, was used to develop a system for physically disabled human to move freely in an environment. We used a camera to get visual information by a human and then arrived information was fed to a computer system. Information was processed with a run time implementation. Control of prototype was inter linked based on user-end data that shows desired direction of movement. Experiments were performed in controlled environment. Limitations and possible future works would also be identified.
    Keywords: Disable, Walking, Hybrid, Robot, Human, Wheel-chair, Control
  • M. Asyaei Pages 699-704
    In this paper, a new circuit scheme is proposed to reduce the power consumption of dynamic circuits. In the proposed circuit, an NMOS keeper transistor is used to maintain the voltage level in the output node against charge sharing, leakage current and noise sources. Using the proposed keeper scheme, the voltage swing on the dynamic node is lowered to reduce the power consumption of wide fan-in gates. Furthermore, the subthreshold leakage current is decreased by using the footer transistor in diode configuration and consequently, the noise immunity is increased in the proposed circuit. Simulation results of wide fan-in OR gates in 90nm CMOS technology demonstrate 48% power reduction and 1.65× noise-immunity improvement at the same delay compared to the conventional dynamic circuit for 32-bit OR gates.
    Keywords: Dynamic Circuit, Keeper, Leakage Current, Noise Immunity, Wide Fan-in Gates
  • C. Z. C. Hasan, R. Jailani, N. M. Tahir, H. M. Desa Pages 705-711
    The characteristics of vertical ground reaction force (VGRF) gait patterns in children with autism spectrum disorders (ASD) are poorly understood. The purpose of this study was to identify VGRF gait features that discriminate between children with ASD and the peer control group. The VGRF data were obtained from 30 children with ASD and 30 normal healthy children aged 4 to 12 years. A three-dimensional motion analysis system with eight cameras and two force plates were used to collect VGRF data while subjects performed self-selected speed of barefoot walking. Parameterization techniques were applied to VGRF waveforms to extract the VGRF gait features. Mean significant differences between the two groups were tested using independent samples t-test and Mann-Whitney U test. Significant group differences were found for four VGRF gait features. Results indicated that children with ASD exhibited a significant reduction of the second peak of VGRF, earlier relative time to the occurrence of the second peak of VGRF, lower push-off rate, and higher peak ratio of the two VGRF peaks during normal speed of walking. These prominent differences showed that children with ASD had difficulties in supporting their body weight during terminal stance phase and these conditions affect the gait instability. The findings of this study develop further understanding of VGRF gait patterns that significantly differentiate between children with ASD and the peer control groups.
    Keywords: Autism Spectrum Disorder, Gait Analysis, Gait Pattern, Ground Reaction Force, Vertical Ground Reaction Force
  • S. Rastani, H. Babai Pages 712-718
    Deposition process for thin insulator used in polysilicon gate dielectric of thin film transistors are optimized. Silane and N2O plasma are used to form SiO2 layers at temperatures below 150 ºC. The deposition conditions as well as system operating parameters such as pressure, temperature, gas flow ratios, total flow rate and plasma power are also studied and their effects are discussed. The physical aspects of the yielded dielectrics such as layer thickness and uniformity are presented as well.
    Keywords: Plasma Deposition, Thin Film Transistor, Display, Process Optimization, Low Temperature Dielectric
  • Z. S. Tabatabaeian, M. H. Neshati Pages 729-733
    In this paper sensitivity analysis of a wideband backward-wave directional coupler due to fabrication imperfections is done using Monte Carlo method. For using this method, a random stochastic process with Gaussian distribution by 0 average and 0.1 standard deviation is added to the different geometrical parameters of the coupler and the frequency response of the coupler is estimated. The applied process must be done several times for converging Monte Carlo method. Therefore, a large number of simulations is reqired for the coupler. This may take a long time if one uses High Frequency Structure Simulator (HFSS) as the simulation software. To decrease the required time of analysis, neural network model of the coupler incnjuction with Mone Carlo is used. Results showed that the bandwidth of the coupler, minimum return loss in passband and minimum isolation in passband won’t be change considerably using the sepecified value of random process. The obtained results for a prototype of a backward wave coupler is presented, which confirm the results of the sensitivity analysis.
    Keywords: Backward-wave Directional Coupler, Neural Network, Monte Carlo Method, Probability Density Function, Cumulative Distribution Function
  • Ran Zhao Pages 734-740
    This paper presents a magnetostrictive in-pipe impact drive mechanism (IDM). To estimate the output performances of the IDM, a dynamics model was developed based on the magnetostrictive material constitutive model and mechanical model of the IDM. Therefore, an experimental system has been built to test the motion performance of IDM. Simulation and experimental results illustrate that the proposed model can accurately predict the step-size of the IDM. The working frequency of the designed IDM is from 10 to 120 Hz, with a the step-size resolution of 740 nm. The magnetostrictive IDM performs good linearity, and can be applied to precision positioning.
    Keywords: In-pipe Motor, Impact Drive Mechanism, Magnetostritive Materials, Impact Inertia Principle, Precision Positioning
  • M. Zadehbagheri, R. Ildarabadi, M. Baghaeinejad Pages 741-751
    Z-Source converter or impedance-source converter is a kind of power converters, which has the responsibility to convert the direct current to alternative current. This converter with respect to its circuit diagram acts as a buck-boost converter except it doesn’t use from DC-DC converter bridge. Γ-source inverters are one of the conventional converters based on impedance-sources; which have been under considerations of professionals at power industries due to enhanced features. These features are contained boost of output voltage level, low number of active and passive elements and low requirement to achieve the high turn's ratio of coupling transformer. This paper dealt with the survey and modeling of gamma power source systems. In this regard, the first dynamic model of converter can be extracted by writing power balance equations. In addition, with the help of dynamic equations converter performance, analysis functionality will be available in various working conditions. Finally, the strategy of proper functioning will be provided for improving the performance of the converter.
    Keywords: Asymmetrical Γ-source Inverters, Improved Y-source, Z-source, Power Conversion System, Modeling, Simulation, Steady State
  • T. Sarkar, S. Pradhan Pages 752-758
    Estimating and minimizing the maximum power dissipation during testing is an important task in VLSI circuit realization since the power value affects the reliability of the circuits. Therefore during testing a methodology should be adopted to minimize power consumption. Test patterns generated with –D 1 option of ATALANTA contains don’t care bits (x bits). By suitable filling of don’t cares can minimize the number of switching activity between two successive patterns. The switching power dissipation of the Circuit under Test (CUT) also depends on the order of patterns applied for. If consecutive pattern application time is sufficiently large then leakage power dissipation does not alter on the ordering of the patterns. So under this circumstances leakage power does not change but if the pattern application time is small leakage power depends on the ordering of the pattern applied to the CUT. Previous works concerns only about don’t care filling or pattern ordering or first filling of don’t care and then ordering for low power circuit testing. Ordering after filling of don’t care may change the benefits of X-filling. The advantage of test power reduction of both the methods - don’t care filling and ordering may be obtained if they are considered together. In this work an approach based on Genetic Algorithm (GA) is used to solve the integrated problem for X-filling and reordering of test patterns considering pattern dependency to minimize the switching activity throughout testing without changing the fault coverage. Effectiveness of the proposed GA based approach compared to existing approach considering test patterns for ISCAS’85 benchmark circuits is shown in the result section.
    Keywords: Testing, Dont care, Run time leakage, Fault coverage, Genetic Algorithm, Test pattern ordering, Pattern dependency
  • A. Mohsenzadehledari, A. Arshadikhamseh Pages 759-769
    In this paper, a three-echelon supply chain , including two producers, distributor and retailer who produce products in different brands have been considered. Any manufacturer, has a separate channel and the exclusive retailer offers their products, which have been prepared from the distributor (exclusive market) with discount or other manufacturer. In this paper pricing decisions on substitute products with different brands on the market has been developed in exclusive and non-exclusive markets for loyal and indifferent customers. The demand for products depend on the distance from brand and ideal product prices. In this model retailer buys product from distributor, but as in the real world ,we face with disruption risk in each channel between the retailer and distributor, only some percentage of orders will be met by distributor and the remains will be done as special orders by manufacturer. The aim of this paper is maximizing the profitability of the entire supply chain, so that optimal selling price to be determined in every channel. Finally, numerical examples and sensitivity analysis have been done on them .
    Keywords: Pricing, Three echelon supply chain, Game theory, Disruption risk, Special order, Brand value, substitute product
  • H. R. Mollaei, R. Tavakkoli-Moghaddam, A. Toloie-Eshlaghy Pages 770-779
    The purpose of this problem is to choose a set of project activities for crashing, in a way that the expected project time, cost and risk are minimized and the expected quality is maximized. In this problem, each project activity can be performed with a specific executive mode. Each executive mode is characterized with four measures, namely the expected time, cost, quality and risk. In this paper, linear relationships between time and cost, and between time and quality are omitted and the problem of the expected time-cost-quality tradeoff is considered in a probabilistic and discrete state. Then, to make the problem more real, the combination of four measures are considered as uncertain for each executive mode. It means that time, cost, quality or risk (or all of them) of each activity in each executive mode is considered as the expected numbers (probabilistic means). After modeling three objective problems, a test problem with nine activities is presented and solved by the NSGA-II algorithm. In order to improve the results and speed of the proposed algorithm in accessing Pareto solutions, a new hybrid algorithm, called MEM-NSGA, is presented that gives better solutions than the NSGA-II algorithm in the same conditions.
    Keywords: Project scheduling, Risk based project planning, Discrete Time–Cost–Quality-risk Trade-off, Evolutionary algorithm
  • H. Farughi, A. Amiri, F. Abdi Pages 780-791
    Project success is assessed based on various criteria, every one of which enjoys a different level of importance for the beneficiaries and decision makers. Time and cost are the most important objectives and criteria for the project success. On the other hand, reducing the risk of finishing activities until the predetermined deadlines should be taken into account. Having formulated the problem as a multi-objective planning problem, the present study aims at minimizing the project completion time as well as maximizing the net present value and project flexibility by taking into account the resource constraints and precedence relations. Here the flexibility of project is calculated by considering a free float for each activity and maximizing the sum of these flotation times. Although most of the researches considered the resources as non-renewable resources, here the resources are considered as renewable ones. Moreover, performing each activity may be possible in various states of using resources (mode) which can change the project completion time and cost. Owing to the complexity of the problem, the Multi Objective Simulated Annealing Meta-heuristic Algorithm is used to solve the proposed model. In doing so, first a feasible answers is proposed and then, using the aforementioned algorithm, it was attempted to find Pareto answers. For accrediting the algorithm, four benchmark problems have been considered. Since the algorithm performed well in finding the optimal answers to the benchmark problems, it was used to find the optimal answer of large scale problems.
    Keywords: Resource constrained project scheduling, Time-cost trade-off, Simulated Annealing meta-heuristic algorithm, Project flexibility, Multi-mode activities
  • M. Akbarzadeh, M.Zandrahimi, E. Moradpour Pages 792-798
    In this investigation, MoSx/Cr coatings were deposited by direct-current magnetron sputter onto Ck45 (AISI 1045) plain carbon steel substrates. The MoSx/Cr ratio in the coatings was controlled by sputtering the composite targets. The chemical characterization was performed using EDX (energy dispersive X-ray analysis); the structural characterization was accomplished by X-ray diffraction (XRD) studies. The mechanical properties of coatings were analyzed by nanoindentation experiments. The tribological behavior of the coatings was investigated using the pin on disc test at room temperature. MoSx/Cr coatings with Cr atomic percentage of 13% was found to possess the optimum wear resistance and durability. The MoSx/Cr coatings showed a maximum hardness of 12.5 GPa at a dopant content of 13 at.% Cr. Moreover, the films exhibited a steady state friction coefficient from 0.15 to 0.19 and the main wear mechanisms of the MoSx/Cr coating in air were abrasive, adhesive, and oxidation.
    Keywords: MoSX-Cr coating, PVD, Tribological properties, Low Friction, Solid Lubricant
  • A. M. Jadidi, M. Jadidi Pages 799-804
    Phase change materials are substances that absorb and release thermal energy during the process of melting and freezing. This characteristic makes phase change material (PCM) a favourite choice to integrate it in buildings. Stephan problem including melting and solidification in PMC materials is an practical problem in many engineering processes. The position of the moving boundary, its velocity and the temperature distribution within the domain are important for these applications. Well known numerical techniques have difficulties with time-dependent boundary conditions. Therefore, fine mesh and small time steps are needed to obtain accurate solutions. There are two main approaches to solve the Stefan problem: front-tacking and variable grid method. The most existing methods are not applicable to all situations and they cannot be easily implemeted in two-dimensional or three-dimensional geometries and all boundary conditions. In this paper, we proposed an algorithm to solve one-dimensional Stefan problem in all kind of boundary condition; also it can be easily extended for 2D and 3D Stephan problems using finite difference method. For validation, the results are compared with exact solution of constant boundary condition. Afterward, periodic boundary condition is considered. The results showed significant relationship between numerical and exact solution, and the maximum error was approximately 0.4%.
    Keywords: Phase Change Material, Numerical Simulation, Finite Difference, Stephan Problem
  • G. V. Pradeep, K. Rama Narasimha Pages 805-811
    This paper presents the experimental investigations conducted on a vertical closed loop pulsating heat pipe (VCLPHP) to evaluate the thermal performance. The values of thermal resistance and heat transfer coefficient obtained in the experimentation is used as evaluation parameters. The VCLPHP used has capillary tubes having an inner diameter of 2mm and outside diameter 3mm and bent into 5 turns. The lengths of the evaporator, adiabatic and condenser sections are 50, 90 and 70mm, respectively. The binary mixture of fluids used are acetone – ethanol and ethanol - methanol mixtures. The thermal performance of these binary mixtures were then compared with conventional working fluids such as acetone, ethanol and methanol. The fill ratios was changed from 50 to 80% in steps of 10% and the heat inputs were varied between 60 to 90W in steps of 10W. However, the mixing proportions for all mixtures was maintained as 1:1. All the experiments were conducted in the vertical position (90°). The experimental results showed that, the overall performance of acetone was the best with the lowest thermal resistance and highest heat transfer coefficient as compared to all pure fluids and among fluid mixtures the acetone-ethanol mixture showed the best thermal performance.
    Keywords: Pulsating Heat Pipe, Binary Mixture of Fluids, Thermal Performance, Thermal Resistance
  • E. Afshari, S. P. Hosseini, M. Mosharaf-Dehkordi Pages 812-819
    The performance of proton-exchange membrane fuel cell cooling system using coolant flow channels enhanced with baffles was numerically investigated. To do this, the maximum temperature of the cooling plate, temperature uniformity and also pressure drop along the flow channels were compared for different cases associated with number of baffles and their dimensions inside the channels. The governing equations by the finite-volume approach in three dimensions were solved. Numerical results indicate that the baffle-restricted cooling flow channels, generally improved the performance of the fuel cell in such a way that a reduced maximum temperature of the cell and a better temperature uniformity in the cooling plates were determined. As the pressure drop increases by incorporating the baffles inside the coolant flow channels, one needs to compromise between the improvement of cooling system performance and the total pressure drop.
    Keywords: Proton-exchange Membrane Fuel Cell, Cooling Flow Field, Baffle, Temperature Uniformity, SurfaceTemperature, Pressure Drop
  • B. Ravi Kumar*, M. K. Saranprabhu Pages 820-825
    In the current study, twin wind blades are designed, fabricated and the effect of various gap ratio (g*) at various angle of attacks (α) on a next to each other twin wind blades are examined in an open-channel wind tunnel. Aerodynamic forces and moments are determined by using three-constraint force balancer. For gap ratio of zero, the aerodynamic attributes are like those of a solitary wind blade edge. As g* increases, these two wind blades actuate the vertical wake to stage vortex shedding modes. With further increment in g*, the wake stream pattern was like those behind a solitary wind blade. For a solitary wind blade, the maximum lift is found to be at α = 30. The pitching moment increases with α. The impact of upper aerofoil blade on the lower one diminished as g* increases.
    Keywords: Rotor, Flow characterization, Aerodynamic Performance, CFD Investigation
  • S. M. Salehi, G. H. Farrahi, S. Sohrabpour Pages 826-833
    Wheel wear has been a concern in the railway for several decades. Studying the form change of the wheel/rail contacts in particular railways consisting of sharp curves helps to identify the risk of severe or catastrophic wear to minimize maintenance costs in order to be competitive in the transportation business. In this paper, the wheel/rail contact was studied on the particular railways. The experimental measurement of wheel profiles was used as an input to Hertz Contact Theory (HCT). It was found that: 1) for these railways the wheel flange is highly worn; 2) a 5th order polynomial function is appropriate to model the wear behavior of the critical wheel; 3) the minimum and maximum contact ellipse surface areas occur in Sd=22.29 mm and Sd=32 mm, respectively; 4) the maximum and minimum surface areas of the contact ellipse occur at points in which the contact pressure are minimum and maximum, respectively; and finally 5) the flange thickness region between 25 to 29 mm can be chosen as an appropriate range for the wheel maintenance purposes.
    Keywords: Wheel Wear, Maintenance Technique, Sharp Curved Railways, Empirical Study, Wheel Flange Wear, Wheel Longevity Enhancement
  • S. Kumar Ghosh, S. Mandal Pages 834-840
    In the present world, energy is indispensable for maintaining the comfort level and living standard of the human. On the other hand, the energy crisis is a major problem in most of the developing countries like Bangladesh. A possible reason is that, the decreasing level of conventional energy sources and the lack of initiatives for introducing the alternative sources of energy. Moreover, the inefficient and illegal way of using energy contributes to the energy crisis. In this study, the present scenario of the electricity generation and its usage in Bangladesh has been investigated. It appears that the increasing amount of battery operated vehicles and their demand for electricity is one of the main reason for energy deficit in the country. The biogas technology as a potential renewable source of energy could be proved as an efficient solution to the energy crisis. For the further studies, a feasibility study is carried out showing that the biogas technology is economically feasible for producing electricity. Moreover, environmental effects, social benefits, and challenges for setting up a biogas plant have been evaluated.
    Keywords: Biogas, Electrical Energy, Livestock, Bangladesh, Auto-rickshaw
  • A. Asgharia, N. Kordani Pages 841-846
    Water cooling by ambient takes place with two mechanisms of heat and mass transfer. Using packings at wet cooling towers has disadvantages such as obstruction, reduction of life expectancy and production of algae and fungi. In shower cooling towers types of towers packings are completely removed and water intake is in direct contact and heat transfer takes place in two ways of latent and sensible. In this article mathematical modeling and simulation of towers has been done using differential equations. Differential equations derived using the laws of conservation of mass and energy. Differential equations is solved in a computer program for numerical solution. The operation of shower cooling towers at different environmental conditions was observed. These towers in the area of cold, dry, warm and dry possess high efficiency. In very hot areas by reducing the drops diameter, the tower outlet temperature can be improved.
    Keywords: Shower Cooling Tower, Heat transfer, Mass transfer
  • V. A. Balogun, I. F. Edem Pages 847-855
    This paper presents an approach to analytically determine the most energy efficient toolpath strategy in mechanical machining. This was achieved by evaluating the electrical energy requirement of the NC codes generated for the zag, zigzag, and rectangular contour toolpath strategies. The analytical method was validated by performing pocket milling on AISI 1018 steel with the considered toolpaths using a 3-axis Takisawa Mac-V3 milling machine. The rectangular contour toolpath was the most efficient in terms of the electrical energy demand of the feed axes and cycle time. Pocket milling with the zigzag toolpath strategy resulted in higher electrical energy demand of the feed axes and cycle time by 2% due to acceleration and deceleration characteristics of the machine tool feed axes execution at corners of the toolpath strategy adopted. Also, the electrical energy demand of the feed axes and cycle time for the zag toolpath were higher by 14% and 8%, respectively, due to the number of tool retracts as a result of the executed toolpath strategy. The experimental validation results showed good agreement with the analytical approach presented in this study. It can be deduced that for sustainable machining, the rectangular contour toolpath should be adopted since it has less tool retractions irrespective of the toolpath strategy adopted for machining. This could further enhance the selection of optimum green parameters by shop floor process engineers for sustainable manufacture of products.
    Keywords: Energy Efficiency, modelling, Machining, Toolpath Strategies, NC Codes, Feed Axes
  • M. Bhandwal, R. K. Tyagi Sikarwar Pages 856-862
    In this manuscript, the experimental setup was designed and fabricated for optimizing the parameters of a catalytic converter of INDICA V2 exhaust system. Three turbulence intensify devices, namely Swirl Venturi, Swirl Blades and Swirl Contour, were close-fitted before the catalytic converter. The heating element is embedded in its body and thermocouples are used for knowing the performance at various temperature. The experiments were carried out with and without devices also with and without heating of catalytic converter. The emission was characterized by various engine speed. The results showed that catalytic converter effectiveness and efficiency increases when close-fitted the devices before the catalytic converter with heating. Among these devices, Swirl Blades was more effective and it reduces the CO and HC emission by 33.86%, and by 30.56% respectively. Flow Simulation of these devices was carried out using finite volume method. The obtained simulation shows that transport coefficient of catalytic converter enhances using these devices because of high turbulence intensity at the inlet of the catalytic converter. This research concluded that the heating of the catalytic converter and using the Swirl Blades device before it reduces the air pollution significantly of diesel engine motor vehicle.
    Keywords: Air Pollution, Catalytic Converter, Gas Emission, Turbulency, CFD, Simulation