Sharif Digital Repository

Zn/Ni nanocrystalline multilayer coatings were electrodeposited using single bath method and switching current densities. Effect of deposition current densities (i1 and i2) and number of layers (n) on composition, surface morphology and roughness, microhardness, phase structure and corrosion resistance of Zn/Ni multilayers were studied and compared with that of single layer. Analyzing and optimizing the influences of mentioned parameters on corrosion resistance of multilayers carried out through Response Surface Methodology. The model based on RSM results demonstrated that improvement in corrosion resistance due to increase in “difference of deposition current densities” was more effective... 

Using Renewable Energy (RE) is growing day by day. We need to locate RE in the best place to maximize energy production and supplier profit. As a result, we propose a novel method for RE location (REL). This model suggests a Data-Driven Robust Optimization (DDRO) for multi-objective REL by considering Risk (DDROMORELR). We consider risk by adding min function in energy and profit objectives (government and supplier objectives). A DDRO approach is added to the model to tackle uncertainty and be close to the real world. We utilize an improved Augmented ε-constraint (AUGEPS2) to solve objectives and produce a Pareto front. We compare problems with DDRO and without considering DDRO, and the... 

In the present work, adsorption of hydrogen molecules over a metal organic framework (MOF-5) has been investigated by using first principles density functional theory (DFT). Different strategies have been applied for improving hydrogen storage, i.e. metal doping, boron substitution and functionalization. The metal atoms used for enhancing hydrogen adsorption include Li, Ca and Sc. It is found that the binding energy between these metal atoms and MOF is not enough to prevent clustering. Therefore a number of carbon atoms are substituted by boron atoms and it is indicated that boron substitution enhances the binding energies, significantly. Also the results reveal that boron substituted MOF... 

In the present work the interaction of hydrogen molecules with perfect, defective and scandium doped polycyclic aromatic hydrocarbon (PAH) has been evaluated. At first the potential barrier for the penetration of hydrogen molecules through PAH structures has been investigated and then the adsorption of hydrogen molecules over PAH structures has been studied. To model the graphene surface for barrier calculations, it is shown that coronene can successfully estimate the graphene monolayer. The barrier height is calculated for perfect and two different defective PAH structures including Stone-Wales (SW) and 585. It is found that PAH even with small defects is impermeable to hydrogen molecules.... 

In the present work, the interaction of hydrogen molecules with defective graphene structures doped by transition metal (TM) atoms is investigated by using first principles density functional theory (DFT). Defective graphene structures include Stone-Wales (SW), 585 and 555-777 and transition metals include early TMs, i.e. scandium (Sc), titanium (Ti) and vanadium (V). It is found that in comparison with the pristine graphene, presence of defects significantly enhances the metal binding. Among three defects, 585 divacancy leads to the strongest binding between graphene and metal. Hydrogen adsorption is then evaluated by sequential addition of hydrogen molecules to the system. The results... 

Hydrogen appears as one of the most promising energy carriers. Hydrogen has the advantage of being the cleanest fuel and as a result it can efficiently help limiting the greenhouse effect. However one of the major barriers for the large scale use of hydrogen, especially in the transportation sector, is hydrogen storage issue. There are four different technologies for storing hydrogen which are as follows: (1) Cryogenic liquid hydrogen (LH); (2) compressed gas storage; (3) metal hydride storage technology; (4) Physisorption methods. Physisorption of hydrogen in novel carbon nanostructures such as carbon nanotubes and graphene seems to be a safe and promising method for storage of hydrogen.... 

The use of more efficient energy consuming devices, which are closely associated with reduction of environmental pollution, has gained significant interest in the recent decades. The reduction of drag coefficient also improves safety and durability of environmental structures subjected to high-velocity fluid flow, and causes the noise and vibration to decrease as well. This paper describes the efficiency improvement in energy management by means of reducing drag coefficient in a practical divergent tubular- truncated cone. Extensive numerical simulations with emphasis on the shape optimization study were performed in order to find minimum drag coefficient for both laminar and turbulent flows... 

This study presents a method for global estimation of joint velocities in robotic manipulators. The authors consider a non-minimal model of a robotic manipulator and design an adaptive observer capable of handling uncertainties in robot dynamics. Smoothness of the dynamics of the proposed observer allows its easy implementation in comparison with non-smooth observers. Dimension of the proposed observer is shown to be at least 3n where n stands for the manipulator's degrees of freedom. This number is less than the dimension of most existing globally convergent adaptive observers. Global asymptotic convergence of state estimates to their true values is achieved under no persistency of... 

This paper gives the design and analysis approaches for the class-E power amplifier with a shunt inductor under the nominal conditions, i.e., zero-current switching (ZCS) and zero-current derivative switching (ZCDS), with taking into account the MOSFET nonlinear output parasitic capacitance at any duty ratio. Although, the class-E ZCS/ZCDS conditions obtained high-efficiency, but the switch-current waveform affected by the slope of the voltage across the MOSFET nonlinear drain-to-source parasitic capacitance during the switch-off state, which restricted the operating frequency. On the other hand, the duty ratio is an adjustment parameter to obtain high-frequency operation. Therefore, the... 

We present a method for global estimation of joint velocities in robot manipulators. A non-minimal model of a robotic manipulator is used to design an adaptive observer capable of handling uncertainties in robot dynamics. Dimension of the proposed observer is shown to be at least 3n where n stands for the manipulator degrees of freedom. This number is less than the dimension of most of existing globally convergent adaptive observers. Global asymptotic convergence of system state estimates to their true values is achieved under no persistency of excitation condition. Smoothness of the dynamics of the proposed observer allows its easy implementation in comparison with non-smooth observers.... 

This paper introduces a new concept that we call smart transmission expansion planning (TEP) based on unconventional high surge impedance Loading (HSIL) line designs that will revolutionize power delivery. To date, these two areas (TEP and transmission line design) have been conducted separately. For TEP, planners use the electrical parameters of a few standard conventional line designs to study planning scenarios, and then, the final candidate line is constructed. In such a sequence, cost-effective scenarios often do not meet the technical criteria of load flow. This paper will demonstrate that this sequence can be overturned; namely, a transmission expansion planner can get optimal line... 

Ultrasonic-assisted machining is an advanced method which could improve the process of machining. Besides, simulation modeling process is a method to help the researchers analyze different aspects of the process with more details in a shorter time. Simulation of ultrasonic-assisted machining is also a field of research that is of interest to researchers working in the field of machining processes. In recent years, a variety of papers have been published where cutting forces, chip formation, tool wear and temperature, and microstructure changes were simulated. That being the case, a review paper is required to represent the advances implemented by researchers in the simulation of... 

Heat exchanger network synthesis (HENS) is one of the most efficient process integration tools to save energy in chemical plants. In this work, a new optimization framework is proposed for the synthesis of HENS, based on a genetic algorithm (GA) coupled with a commercial process simulator through the ActiveX capability of the simulator. The use of GA provides a robust search in complex and nonconvex spaces of mathematical problems, while the use of a simulator facilitates the formulation of rigorous models for different alternatives. To include the most common heat exchanger structures in the model, a promising superstructure has been used. Allowing nonisothermal mixing of streams in the new...