Sharif Digital Repository

In this work we show how Artificial Intelligence (AI) could effectively be used to expedite the decision making process in the early stages of the aircraft design process. We employ both Fuzzy Logic (FL) and Neural Network (NN) as two different schemes of the AI. The developed tools are intended to help to select the proper combination of engine thrust, wing area and the aircraft weight without going through elaborate details of other direct approaches. We further show how the AI could be applied to the specific class of light business jets which serves to validate these schemes. The results indicate the effectiveness of the AI approach in the preliminary aircraft design process. The actual... 

In this study, the effects of simultaneous co-deposition of polytetrafluoroethylene (PTFE) and MoS 2 particles on tribological properties of electroless nickel (EN) coating were studied. The influences of specimen orientation and heat treatment on EN-PTFE-MoS 2 composite coatings were also investigated. Scanning electron microscopy was used to study the morphology of coatings and the distributions of the lubricant particles in the deposits. Chemical analyses of coatings were done by electron dispersive spectrometry. The phases of the coatings were identified by X-ray diffraction utilizing CuKα radiation. Wear and friction properties of the coatings were also determined by pin-on-disk wear... 

A large number of generators failed due to stator winding problems, mainly insulation deterioration. Insulation degradation assessment plays vital role in the asset life management. Electro thermal analysis is the main characteristic for simulation of generator behavior and to improve the design of stator slot's insulation. Dielectric parameters such as insulation thickness, spacing, material types, geometry of winding and slot are major design consideration. A very powerful method available to analyze electro thermal performance is Finite Element Method (FEM) which is used in this paper. The analysis of various stator coil and slot configurations are used to design the better dielectric... 

In this paper, the problem of formation control with regard to leader–follower mobile robots in the presence of disturbances and model uncertainties, without needing to know the velocity of the leader robot, is presented. For this purpose, at first, a first-order kinematic model of leader–follower and leader–leader formations is obtained, and considering the absolute velocity of the leader robots as an uncertainty, a robust adaptive controller is designed to keep the desired formation. In this case, the upper bound of uncertainty is unknown and is obtained via stable adaptive laws. Afterwards, in order to deal with the accelerated robots and obstacles, second-order leader–follower and... 

Heteropoly acid was found to be an effective and efficient catalyst for the ring opening reaction of epoxides with various aromatic amines to produce the corresponding β-amino alcohols in moderate to excellent yields in water. This method provides a new and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple work-up procedure  

A simple, rapid, atom economy and highly efficient procedure has been developed for thiolysis of epoxides by aromatic and aliphatic thiols under solvent-free conditions. A high regioselectivity in favor of nucleophilic attack at the benzylic carbon atom of aromatic epoxides, such as styrene oxide, is observed. However, aliphatic unsymmetrical alkenyl oxides undergo selective nucleophilic attack at the sterically less hindered carbon atom. A variety of β-hydroxy sulfides were obtained in short reaction time and excellent yields with nearly complete regioselectivity  

The effect of vehicles’ compatibility on the odds of death or injury of drivers involved in two-vehicle crashes was investigated. This was done through indexing Crashworthiness (CW) and Crashaggressivity (CA) of major vehicle types. For this purpose, a dataset consisting the information about 551,138 drivers involved in two-vehicle crashes in Iran was used and a two-step analysis framework was employed. In this regard, the Classification and Regression Tree (CART) method was applied in the first step to identify the most significant factors contributing to drivers’ Injury Status (IS). Next, Generalized Estimating Equations (GEE) with a Binomial distribution and a Logit link function were... 

The effect of vehicles’ compatibility on the odds of death or injury of drivers involved in two-vehicle crashes was investigated. This was done through indexing Crashworthiness (CW) and Crashaggressivity (CA) of major vehicle types. For this purpose, a dataset consisting the information about 551,138 drivers involved in two-vehicle crashes in Iran was used and a two-step analysis framework was employed. In this regard, the Classification and Regression Tree (CART) method was applied in the first step to identify the most significant factors contributing to drivers’ Injury Status (IS). Next, Generalized Estimating Equations (GEE) with a Binomial distribution and a Logit link function were... 

The effect of vehicles’ compatibility on the odds of death or injury of drivers involved in two-vehicle crashes was investigated. This was done through indexing Crashworthiness (CW) and Crashaggressivity (CA) of major vehicle types. For this purpose, a dataset consisting the information about 551,138 drivers involved in two-vehicle crashes in Iran was used and a two-step analysis framework was employed. In this regard, the Classification and Regression Tree (CART) method was applied in the first step to identify the most significant factors contributing to drivers’ Injury Status (IS). Next, Generalized Estimating Equations (GEE) with a Binomial distribution and a Logit link function were... 

The compaction forming of metal powder is a process involving large deformations, large strain, non-linear material behavior and friction. Consequently, the numerical analysis of such a highly non-linear process is a formidable computational problem. In this paper, an ALE technique is presented based on a generalized cap plasticity model in simulation of powder forming processes. In ALE formulation, the reference configuration is used for describing the motion, instead of material configuration in Lagrangian, and spatial configuration in Eulerian formulation. This formulation introduces some convective terms in the finite element equations and consists of two phases. Each time step is... 

The effects of milling time and annealing temperature on phase formation, microstructure and magnetic properties of nickel-cobalt ferrite synthesized from oxide precursors by mechanical alloying were studied. The study of milling time effects on phase formation of milled materials showed that if milling continues up to 55 h, single phase nano-sized nickel-cobalt ferrite is obtained. Also, magnetic properties of powders versus milling time and annealing at different temperatures extensively changed, so that annealing at 1200 °C increased the magnetization saturation of the as-milled powder from 15.1 to 53.6 emu/g. X-ray powder diffraction technique (XRD) with Cu-Ka radiation was employed for... 

Based on the observation that dynamic occurrence of zeros in the cache access stream and cache-resident memory values of ordinary programs exhibit a strong bias towards zero, this paper presents a novel CMOS five-transistor SRAM cell (5T SRAM cell) for very high density and low power cache applications. This cell retains its data with leakage current and positive feedback without refresh cycle. Novel 5T SRAM cell uses one word-line and one bit-line and extra read-line control. The new cell size is 17% smaller than a conventional six-transistor SRAM cell using same design rules with no performance degradation. Simulation and analytical results show purposed cell has correct operation during... 

Observability of bulk power transmission network by means of minimum number of phasor measurement units (PMUs), with the aid of the network topology, is a great challenge. This paper presents a novel equivalent integer linear programming method (EILPM) for the exhaustive search-based PMU placement. The state estimation implemented based on such a placement is completely linear, thereby eliminating drawbacks of the conventional SCADA-based state estimation. Additional constraints for observability preservation following single PMU or line outages can easily be implemented in the proposed EILPM. Furthermore, the limitation of communication channels is dealt with by translation of nonlinear... 

Based on the observation that dynamic occurrence of zeros in the cache access stream and cache-resident memory values of ordinary programs exhibit a strong bias towards zero, this paper presents a novel CMOS four-transistor (4T) SRAM cell for very high density and low power cache applications. This cell retains its data with leakage current and positive feedback without refresh cycle. The new cell size is 20% smaller than a conventional six-transistor cell using same design rules and delay access of a cache based on new 4T SRAM cell is 32% smaller than a cache based on 6T SRAM cell. Also the dynamic and static power consumption of new cell is 40% and 20% smaller than 6T SRAM cell,... 

Delay and especially delay in the transmission of agents’ information, is one of the most important causes of disruption to achieving consensus in a multi-agent system. This paper deals with achieving consensus in delayed fractional-order multi-agent systems (FOMAS). The aim in the present note is to find the exact maximum allowable delay in a FOMAS with non-uniform delay, i.e., the case in which the interactions between agents are subject to non-identical communication time-delays. By proving a stability theorem, the results available for non-delayed networked fractional-order systems are extended for the case in which interaction links have nonequal communication time-delays. In this... 

The leakage current and process variation are drastically increased with technology scaling. In Conventional SRAM cell due to process variations, stored data can be destroyed during read operation. Therefore, leakage current of SRAM cell and stability during read operation are two important parameters in nano-scaled CMOS technology. To overcome these limitations and to increase the speed of conventional SRAMs, we have developed a read-static-noise-margin-free SRAM cell. The developed cell has six-transistors and uses two read/write-lines and two read/write-bit-lines during read/write operation. This cell retains its data with leakage current and positive feedback without refresh cycle. The... 

The process of fluid flow displacement in porous media has recently gained great prominence owing to its widespread usage in a variety of industries, especially in the case of pore scale investigations. Although, many studies have been conducted to address pore-scale investigations in both modeling and experimental approaches, the role of interfacial tension and contact angle on pore-scale phenomena is less focused. In this work, direct pore-scale modeling was used to precisely examine the effect of interfacial tension and contact angle on the fluid flow at the microscale. Also, several pore-scale mechanisms, including Haines jump and dynamic breakup mechanisms, were observed. Therefore, the... 

Electric distribution network is undergoing fundamental transition from conventional top-down structure to an environment where local prosumers, as transactive agents, are able to form peer-to-peer (P2P) energy trades among themselves. One of the challenges in such networks is allocating the incurred losses to the peers of the transactive market through a transparent and fair framework. In this article, it is demonstrated that the existing methods of loss allocation may cause a cross-subsidization problem when it comes to transactive energy systems, and a solution is offered to the problem. Furthermore, a novel transactive market mechanism is proposed which deploys the loss allocated to each... 

In this study, an industrial acetylene hydrogenation unit is simulated utilizing three available kinetic models. The results are compared against six-day experimental data and the best model is selected. Effects of feed temperature and the amount of injected hydrogen on ethylene selectivity are also studied. According to the simulation results, the unit is not working under its optimum conditions. Furthermore, by reduction of the hydrogen flow rate to 52 kg/h, process selectivity is increased. In addition, a new approach is proposed to modify the hydrogenation process and reduce undesired by-products. In the simulation of the modified process, hydrogenation reactors temperature, hydrogen... 

In the present work, an unsymmetric laminated plate with surface bonded piezoelectric sensors, and actuators has been considered. Piezoelectric sensor were used to monitor the load and deformation bifurcation occurs. Monitoring the shape and load of a morphing structure is essential to ascertain that the structure is properly deployed and it is not loaded excessively, thus, preventing structural to failure. A piezoceramic actuator is used to provide activation load and to force the structure to change its stability state from one to another. A non-linear finite element model based on the layerwise displacement theory considering the electro-mechanical coupling effects of piezoelectric...