Sharif Digital Repository

In this project, the equilibrium structure of clamped-free silicon nano-beams is investigated using molecular dynamics (MD) simulations. Four main interatomic potentials for silicon nanostructures, i.e. Tersoff, MEAM, Stillinger-Weber and EDIP, are implemented in the current study. Using aforementioned potentials, the structural stability of Si nano-beams are studied and effects of thickness, width, length, size, lattice direction, facets of cross section, and temperature on the equilibrium structure of nano-beams are investigated. The conducted simulations demonstrate that equilibrium structure of nano-beam is completely dependent on the type of atomic potential used for modeling.... 

Atomic force microscopy (AFM), as an indispensable tool for nanoscale characterization, has major drawback for operation in a liquid environment arising from the large hydrodynamic drag on the vibrating cantilever. The newly introduced “Trolling Mode” (TR-Mode) AFM resolves this complication utilizing a specialized nanoneedle cantilever that keeps the cantilever outside of the liquid. Herein, a mechanical model with a lumped mass was developed to capture the dynamics of such cantilever with a nanoneedle tip. This new developed model was applied to investigate the effects of the needle – liquid interface on the performance of the AFM, including the imaging capability in liquid. Also... 

Submerging of the Micro-beam of the AFM is indispensible in case of imaging bio-samples. (Bio-samples are unstable in non-aquos environment.), so hydrodynamical interaction of liquid and beam (viscous and meniscus forces) will result into quality factor decrease. This will cause image resolution decrement as well as damage to the sample because of large tip-sample forces during imaging of the bio-samples. The proposed method “Trolling mode AFM” keeps the micro-beam of the AFM out of the liquid, by adding a nano-needle to the end of the AFM tip. This would lead to resolve the aforementioned problems. Modeling of a part of the operation of this mechanism was done in this thesis, in order to... 

In this research, we aim to study and simulate how nanoparticels translocate through cell membrane. For this purpose, at first a gold nanoparticle is selected as the drug carrier. The partial charges of the ligands are calculated using quantum mechanics based on HF technique with 6-31Gd basis set. To have a realistic shape for nano drug, number and arrangement of ligands are determined based on optimization. After all atom simulations and comparison of results such as diffusion coefficient with experiments, a coarse-grained model of these drugs is created and put inside solvent beside a membrane. The cytoplasmic membrane includes more than 60 types of phospholipids like animal membranes.... 

Micro-robotics is one of the currently emerging technologies which has attracted attentions for its probable applications in different fields including biotechnology, diagnosis and treatment in medical engineering as well as general studies in micro-scale science and engineering. Magnetic micro-robotics is considered as the most promising group, primarily due to the biocompatibility of magnetic fields and advances in electronic circuits to produce and control such fields. One critical point in utilizing these robots is their high density in comparison with the working fluid and their tendency to sink. In this thesis, a method to fabricate buoyant magnetic robots has been proposed based on... 

Nanopositioning is technology of positioning & manipulation of Nano-scale object. This technology can be considered as one of the fundamental necessities in Nano & Micro research and fabrication and made lots of unbelievable advancement in researches and technologies. There are lots of mechanical systems designed for large scale positioning with sub millimeter resolution, but when it’s come to Nano scale, the range of access should be limited to some micrometer. Also in Nano-scale motion some difficulties like backlash, stick-slip and friction is phenomenon. For increasing the workspace using coarse and fine positioning systems may be an appropriate method. In this method a fine positioning... 

Endoscopy is a medical operation in which a camera is sent into the patient's body and the physician starts taking pictures at specified times. In the traditional endoscopic procedure, a camera is sent into the body by a guiding wire. This can cause severe pain to the patient. In the newer method, a camera is mounted on a small capsule and the patient swallows the capsule. Then the camera inside the capsule starts taking photos and sends them out. This procedure, in addition to being painless, allows the physician to access the innermost parts of the body or the digestive tract.In capsule endoscopy, unlike the older method, one has to find the position and orientation of the capsule at any... 

Minimally invasive procedures are diagnostic or therapeutic methods that cause minimal injuries and side effects for patients. PCI is a common minimally invasive procedure for diagnosis and curing of cardiovascular disorders. In this procedure, the surgeon can have access to the cardiac vessels by a flexible instrument. However, motion control of this instrument inside the patient's body relies on surgeon's skills and in some cases, is time consuming so that the toxic effects of radiation on patient and surgical team increases. Magnetic flexible instruments are suggested to address this problem. Nevertheless, motion control of the flexible instrument inside the body still has many challenges... 

Being harmless to living tissues makes magnetic robots very promising for medical applications. Furthermore, since these robots are driven by external magnetic fields, no actuators are needed to be placed on the robots, enabling them to come in very small dimensions if necessary. Motion control of small magnetic particles paves the way for future applications, such as deliberate drug-delivery, sampling, and lowinvasive surgeries.The goal of this research is to design and construct a platform for generating desired magnetic fields in order to control the motion of magnetic robots in threedimensional space. In order to do so, a system of eight electromagnetic coils with iron cores was built.... 

Today, the need to access very small environments is felt in various medical, industrial, biological and military fields. Due to their small size, microrobots have the ability to perform tasks that would be very difficult to do on a larger scale, but this ability of microrobots makes feeding and controlling them challenging. There are several methods for providing power and control of microrobots, which include their internal or external stimulation, among which the magnetic stimulation method is used in this research, which does not cause damage to body tissues.In this thesis, an electromagnetic system with nine cylindrical coils is used to control the three-dimensional movement of magnetic... 

Minimally invasive surgery is highly valued mainly due to the reduction of the patient’s recovery period. Catheters are among the most important tools in minimally invasive surgeries. Catheter is a flexible tool that has the ability to pass through difficult paths. In common localization methods, fluoroscopy is used to determine the position of the catheter’s tip. One main disadvantage of this method is that it is very dangerous for therapists who are exposed to X-ray radiation for long periods of time. A magnetic catheter is created by adding a magnet to the end of the catheter. The possibility of guiding magnetic catheter by an external magnetic field, controlling the applied force and... 

This thesis is devoted to the simulation of biomolecules manipulation using Molecular dynamics (MD). In order to investigate the manipulation behavior, we have used the Ubiquitin as biomolecule, a single-walled carbon nanotube (SWCNT) as manipulation probe, a graphene sample as substrate. Along this line, a lot of simulations are conducted to study the effects of different conditions on the success of manipulation process. These conditions include tip diameter, vertical gap between tip and substrate, initial orientation of protein, and the simulation environment (dry or wet). The results demonstrate that tips with bigger diameters and smaller distances with respect to the substrate increase... 

In this study, chapter 1 is dedicated to GEO satellites. In chapter 2, slosh dynamics of fluid and its governing dynamical equations are investigated due to the importance of this phenomena in geostationary transfer orbit. In chapter 3, dynamics of satellite orbit and satellite attitude are investigated and governing equations are derived by considering these effects: orbital noise (e.g. shape of earth, gravitation of sun and moon), moment noise (e.g. slosh dynamics of fuel and oxidizer, and liquid apogee motor misalignment). Following the third chapter, some simulations are carried out before the implementation of controllers. In chapter 4, a PID controller and a classical fuzzy controller... 

In this project the main aim is to model the interaction between the cytoskeleton and cell membrane. In order to model the membrane and cytoskeleton it is used a discrete model, which contains several beads. For modeling the interaction between the beads it is used different kinds of energies. It is used four potentials in a 2D model for modeling the interaction between the membrane beads and it is used SSLJ potential in order to model the interaction between the cytoskeleton and cell membrane. Furthermore, this potential is used to model the interaction between the cytoskeleton filaments. Due to this potential, the cytoskeleton filaments can cross each other in the 2D model. For modeling... 

Nowadays, nano-positioners play an important role in advanced technologies, such as atomic force microscopy, genetic manipulation, nano-metrology, nano-fabrication, semi-conductors and etc.In this paper, a dynamical model has been derived for a nano-positioner. This nanopositioner was designed and fabricated in Sharif university of technology. In this paper the mentioned mechanism has been considered as a planar mechanism. First, a finite element model has been developed in Comsol multi-physics software. This model was used as the reference model in the next steps. Afterward, a 10 degrees of freedom model was proposed to estimate the Comsol model. The mass, stiffness, as well as damping... 

One of the most significant aerial vehicles which has been subject of study of so many engineers and students is quadrotor or quadcopter, which is a cross sectional configuration of motors and propellers. This aerial robot is controlled through slight differences between the angular velocities of the four motors, and robot dynamics is completely nonlinear, thus sophisticated control algorithms are needed. The aim of this project consists of design, fabrication and control of a quadrotor capable of stable hovering. First, some preliminary decisions about general charachteristics of the robot were made. According to these decisions, other mechanical parts were designed and fabricated. Then,... 

Providing energy for small but out-of-access devices has led industries to harvest energy from the environment, especially environmental vibrations. The problem of vibrational energy harvesters with linear behavior, is their small bandwidth and consequently, their high sensitivity to frequency content and excitation spectra. Particularly in random excitations with vibrational energy spreading over a frequency range, linear harvesters do not seem appropriate. Under these conditions, harvesters with nonlinear stiffness are possible substitutes for linear systems. However, prediction and estimation of the behavior of systems with nonlinear stiffness under random excitation has been complicated,... 

Humans can take lots of advantages from influencing on small particles. Since manipulation of micro sizes by humans or macro robots, due to their precession and size, is not possible, a new field of study, called Microrobotics, has been introduced. To better understand the working principles in small dimensions, we first need to know the governing physics laws. This step helps us to identify the dominant forces in the small dimensions, which, in turn, leads to better actuation of miniature robots. Because of the size of the miniature robots, one of the best actuation methods is the interaction of the magnetic field on magnetic dipoles. To use the magnetic field as an actuation force, the... 

In this study, the attitude control of an under-actuated satellite has been investigated. The investigated satellite uses reaction wheels for attitude control. For having full controllability of a satellite attitude, at least three reaction wheels are required. However, due to the high failure rate of reaction wheels, in this study assumed the satellite has two perpendicular reaction wheels, which causes the satellite to be under-actuated. The path planning method is used for controlling the satellite, which is an offline method. In the beginning, tries to define the control input of the satellite in term of limited parameters with different methods. In this regard, the control input is... 

It is well-known that helicopters descending fast may enter a region in the velocity space called Vortex Ring State where the blade’s lift differs significantly from regular regions and includes high amplitude fluctuations. These fluctuations may lead to instability and therefore, this region is avoided, typically by increasing the horizontal speed. However, this region is not fully identified for multirotors, which their blades are rigid in contrary of helicopter’s blades which have two degrees of freedom. This project researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel...