Sharif Digital Repository

With respect to the introduction of bio-material into cells (transfection) , microinjection is a highly efficient technique amongst existing methodologies. In cell injection, a manipulator injects the needle into a cellwhich is hold by a pipet mechanism. The moving range for the needle in this operation is of centimeter order and the resolution for the needle tip should be less than the cell’s diameter. In this thesis a Stewart system is used as for the manipulator. Stewart systems are used in flight simulators systems for decades, as mechanisms which are capable of providing multi-axis movements. In high accuracy positioning and multi-axis applications Stewart systems are highly reliable.... 

Microelectromechanical have wide application in mechanic, aerospace, medical, transport and information technology.
Due to large scale application and production, low costs and low energy consumption, these systems have been used in wide range of fields of engineering. Electrostatically actuated microbeams are extensively used as microelectromechanical systems (MEMS) such as microswitch and microresonator. The main component of electrically driven is microbeam. Microbeam acts as top surface of a capacitor with fixed bottom. The capacitance of capacitor changes due to the deflection of the microbeam. In this study static deflection of electrostatically actuated microbeam has been... 

Vibration is one of the most important factors in design, operation and lifetime of drill string. Evaluation of vibration in the drill string like other rotating machines is very important and according to the length of drill string, whirling is one of the issues discussed. The aim of this thesis is non-linear analysis of the oblique long drill string. By considering the effects of passing drill mud around drill as well as properties of the drilling mud and stick - slip effect in creating whirling. Therefore, the equations related to kinetic and potential energy of a rotating drill string by taking longitudinal and transverse vibrations are written and by using the Lagrange method, equations... 

Nano/Microelectromechanical systems have generated a great impact on industry and technology. There are many applications for these systems in micropumps, airbag accelerometers and inkjet printer heads. In theses systems mechanical and electrical fields are involved with each other, and complexities due to this involvement has prevented the scientific society from an effective tool for analysis of this systems in computational point of view. So the objective of this project is to use the Extended Kantorovich method to solve the equations of microplate deformation due to electrostatic actuation. This method is based on variational principals and it uses an initial guess function which doesn’t... 

Micro and nano electromechanical systems technology has experienced lots of progress in recent years. These systems are widely used in sensors and actuators due to their small size low weight and low energy consumption. Electrostatically actuation is one of the simplest and most prevalent methods of actuation and sensing in these systems. Electrostatically actuated micro and nanobeams are used in many devices such as micro and nano switches, resonators, signal filters, tunable capacitors, pressure and mass sensors, etc. Experimental results and measurements have shown that classical theories contain error in prediction of static and dynamic ... 

Red Blood Cells (RBCs) are the main cells in human blood with a main role in mechanical properties of blood as a fluid. Several methods are developed to simulate the behavior of RBCs motion and deformation in micro-capillaries. Since in microscopic scales, using discrete models are more preferred than continuum methods, moving particle semi-implicit method (MPS) which is one of the recent innovative particle based methods, can simulate micro-fluidic flows based on Navier-Stocks equations. Although by the recent developments MPS method has turned into a considerable tool for modeling blood flow in micro-scales, but still some problems, such as commitment to use small time steps, restrict the... 

In recent years, Total Knee Replacement is a highly common surgery. Other than the injuries caused by trauma in accidents among different ages, a need for Total Knee Replacement can arise due to diseases such as Knee Osteoporosis among the elderly which leads to loss of balance in the physiologic properties of knee joint and a failure in load transfer from distal femur to proximal tibia. Currently, the practice of Total Knee Replacement is performed by implanting a mechanical knee between femoral and tibial shafts. Increase in life expectancy of the people with replaced knee, causes the failure of some prostheses due to various factors. Following the failure, a second operation is required... 

A microbeam, actuated by electrostatic distributed force, is a flexible beam-shaped element attached to a fixed rigid substrate. Electrostatically actuated microbeams are extensively used in different applications such as signal filtering and mass sensing. When the input voltage exceeds a critical value, called pull-in voltage (V_pi), the flexible microbeam spontaneously deflects towards the rigid plate. Pull-in instability is a basic phenomenon considered in the design of the micro actuators. When the rate of voltage variation is low and consequently inertia has almost no influence on the microsystem behavior, the critical value of voltage is called static pull-in voltage (V_pi). However,... 

Characterization and simulation of carbon nanotube-reinforced composites at large scale have been a concern of researchers in the past decade. This is due to the computational complication of considering many embedded carbon nanotubes (CNTs). However a simple meshing of organized CNT distribution in the matrix can ease this obstacle. In this study, a finite element approach is employed to investigate the elastodynamic behavior of a wavy CNT-reinforced composite structure. A three dimensional structure with up to 6400 uniformly distributed wavy CNTs is embedded in a polymer matrix. Each wavy nanotube is represented by a set of beam elements. The effect of nanotube waviness and volume fraction... 

The important role of MEMS devices in optical system has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical systems (MEOMS), which mainly includes micromirrors and torsional microactuators. These devices have found variety of application in optical switches, display, micro scanning mirrors, optical cross-connects interferometry, spectroscopy, aberration correction and biomedical imaging. In this project, the dynamic behavior of electrostatic micromirrors under the effect of intermolecular surface forces and squeezed film damping are studied. The prior art published in the literature have mainly used pure torsion models. In a pure torsion, just the torsion... 

Nowadays cancer has become one of the main and prevailing worldwide challenges in medical field, and many attempts have been made for treatment of this disease. The common methods for cancer treatment, have had significant side effects and even resulted death. The method of “High Intensity Focused Ultrasound” (HIFU) as a non-invasive method, has been welcomed by engineers and doctors and is using in some tumor based cancers. For predicting the level of temperature increasing in tissue, it’s necessary to model the ultrasound waves propagates from HIFU source precisely. The main object of this thesis is modeling and simulation of the behavior of ultrasound wave propagation and investigating... 

The application of acoustic waves as a diagnostic tool in medicine is highly regarded. Because of the mechanical and Noninvasive nature of this waves when penetrate in the body will not have any adverse effects on the body. Thus development and operation of these waves is growing every day. If abnormal changes in soft tissues (such as tumors inside the body) is created, by the reflected sound waves easily recognizable although it is experimental, and a little scientific studies have been conducted on the contrast of soft tissue and acoustic waves. Soft tissues of the human body Because of the asymmetric structure has a non-uniform physical and mechanical properties in different directions,... 

Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. This phenomenon has been under study for many years and yet it remains a question due to physiological, geometrical and computational complexity. Due to limitation in experimental study on human head, the finite element human head model with precise geometric characteristics and mechanical properties is essential. In this study, the visco-hyperelastic parameters of bovine brain extracted from experimental data and finite element simulations which validated by experimental results. Then a 3D human head including brain, skull, and the meninges is modeled using CT-scan and MRI data... 

In recent years, functionally graded materials (FGMs) has widely used in many industrial products. FGMs are advanced non-homogeneous materials with mechanical and physical properties that vary continuously as a function of position within the materials. The main goal of this project is to study the static behavior and vibrational analysis of the FGMs spherical structures. In this project, the finite element method is used to do static and dynamic analysis of FGM hollow spheres. A new spherical super element has been designed to enhance modeling of hollow spheres and ease the solution of the finite element model. The deformations due to various static loadings are obtained. The natural... 

Membrane proteins aggregation is a very important biological phenomenon in a variety of cell functions. It has been suggested that aggregation behavior of membrane proteins is influenced by the shape of the hydrophobic domain of the proteins, proteins hydrophobic mismatch and bilayer curvature. However, in this study by means of coarse grained membrane simulations it has been found that in thermal equilibrium, protein-protein interactions also depend on protein rigidity and structural strength. Based on simulation results, we have observed stable large clusters even in the absence of hydrophobic mismatch between lipids and proteins. Interestingly, our results also indicate that proteins with...