Sharif Digital Repository

The actuation mechanism of the tip of an endoscopic instrument is a major problem in designing miniature scale motorized instruments, especially when a high level of functionality and multi degrees of freedom (DOF) are concerned. We evaluated the different possible actuation methods for an endoscopic needle holder and proposed a new design of hybrid local-actuation, including a micro DC motor and a piezoelectric (PZT) actuator. The DC motor provided the long movement course required for opening-closing function of the gripper while the PZT guaranteed the high gripping force required for holding the needle. A compact serial configuration was considered for the actuators, producing an overall... 

A multiscale FD-KMC model has been developed to simulate the cyclic voltammetry test of a copper electrode in simple copper sulfate bath. In this coupled model, the FD code provides the cupric ion concentration on OHP for KMC code, while the KMC code provides the electrochemical properties of the copper electrode (surface activity and rate constants of redox reactions) as an input data for FD code. The changes in the electrode properties due to the atomistic phenomena (deposition dissolution and surface diffusion) have been studied for the present potentiodynamic system. The results showed that the CV process consists of some distinct stages, so that the electrode exhibits a specific... 

A novel method is used to link a 2D kinetic Monte Carlo code to a 1D finite difference code to construct a more realistic and efficient tool for simulating various electrochemical processes. This multiscale model is able to simulate the long-scale mass transfer of electroactive species in bath along with electrode surface phenomena at atomic scale simultaneously. An embedded atom method (EAM) has been used to evaluate the barrier energies of diffusion and redox reactions on electrode surface. The FD code provides the ion concentration on OHP for KMC code, while the KMC code provides the surface activity and rate constants of redox reactions as an input data for FD code. The electrochemical... 

Many important public buildings have suffered significant damages due to terrorist attacks in the last few decades. This paper investigates the behavior of structures with steel plate shear wall lateral load resisting system under various blast loadings. A number of twenty steel frames with different heights and widths subjected to four different blast scenarios are modeled and analyzed in opensees software. The results showed that structures with steel plate shear wall systems subjected to blast loading have better behavior in high-rise structures than in low-rise structures in terms of drift and ductility ratio. The steel plate shear wall system exhibited shear-dominated,... 

Anodic aluminium oxide films were fabricated by well known two-step anodizing process in oxalic acid electrolyte. The ordering characteristics (ordered pore domains, average pore diameter size and through-pore arrangement) of anodic aluminium oxide films, obtained in different growth sequences, were identified by microscopic analysis such as ex situ contact-mode atomic force microcopy and scanning electron microscopy. Flattened areas in which some pits are seen mostly cover the electropolished surface of aluminium. Single anodizing of aluminium produces a broad distribution of nanopore size, whereas induces a highly ordered hemispherical pattern, which plays the ordered nucleation sites for... 

Anodic aluminum oxide (AAO) was used as a template to prepare highly ordered Ni-Fe-Co alloy nanowire arrays. This membrane was fabricated with two-step anodizing method. It is found that there is an optimum barrier thickness to obtain a successful electrodeposition in pores of AAO. The thickness of barrier layer can be modified by additional electrochemical process after completing the anodizing step. Barrier layer thinning can create a rooted structure at the bottom side of the AAO pores and the electrodeposited nanowire arrays. The triple Ni-Fe-Co alloy was deposited in AAO membrane by ac voltage in a simple sulfate bath. The composition of nanowires shows anomalous deposition features... 

Gravity drainage is known to be one of the most effective methods for oil recovery in fractured reservoirs. In this study, both free fall and controlled gravity drainage processes were studied using a transparent fractured experimental model, followed by modelling using commercial CFD software. The governing equations were employed based on the Darcy and mass conservation laws and partial pressure formulation. Comprehensive examination was done on variables such as fluid saturation, velocity, and pressure distribution in the matrix and fracture, as well as fluid front level and production rate. Additionally, effects of the model parameters on the gravity drainage performance were... 

Optimization of a structure refers to a design procedure that results in the most economical structure in terms of materials and sizing of sections. In structures with steel plate shear walls, finding the best layout of the walls in a frame is also of priority in designing a structure with the minimum weight. Finding the least weight of a structure while all design provisions according to codes and standards are satisfied is a challenging task that is hard to perform with the existing design methods. Metaheuristic optimization algorithms are robust computational tools used for solving complex problems, which are used widely in many engineering fields, especially structural engineering. This... 

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...