Sharif Digital Repository

In this study, the seismic response analysis of a buried pipeline had been performed using three-dimensional (3D) dynamic analysis of the soil-pipeline interaction under different loading inputs. A number of parameters such as properties of the buried pipeline including diameter and internal pressure and different loading frequencies were used for this investigation. The pipe was considered as an elastoplastic material and a nonlinear elastic material based on the Mohr–Coulomb criterion was used to model the soil behavior. In addition, pipe-soil interaction has been studied in both tangential and vertical directions. The ABAQUS software was utilized for the 3D numerical modeling and... 

Optimizing optical tweezers and achieving powerful traps has always been a challenging topic for researchers , since the trap stiffness increases with increasing laser power which may damage specimens , especially biological ones and cells . In this thesis , we introduce a special geometry and structure of particles that , have the possibility to increase the stiffness (strength) of the optical trap and cause the magnetic response of particles at optical frequencies . Special geometries such as a combination of dielectric particles with magnetic nanoparticles that emphasize the role of the laser magnetic field and lead to changes in the electrical and magnetic properties at the laser... 

Nowadays, according to increasing development of construction industry in the world especially in the building area, the need to use technology and innovation for fabrication and maintenance of this industry has increased. And this fact becomes apparent that the use of traditional systems of construction isn’t tailored the countries’ requirements anymore. One of the construction industry’s limitations is the restrictions on architectural designs reys. The columns are among the most important components of structure and have a major role in bearing all gravity and lateral loads and transferring them to the foundation. The failure or destruction of the components in the structure under applied... 

Optical tweezer is a highly focused laser beam that could be used to trap micro and nano particles in three dimensions. It could be used to measure(or apply) piconewton range forces. Most of the optical tweezers experiments have been done in liquid mediums. In last few years, trapping particles which are floating in gas mediums(called aerosols) have been considered extensively. In this thesis, the changes in trap stiffness and conversion factor due to changes in laser power, trapping depth and particle are evaluated. It is shown that changing these three parameters, cause considerable changes in trap stiffnes and conversion factor. Linear behavior of trap stiffness versus laser power,... 

One of the main requirements in today’s computer networks such as the Internet is protecting the privacy of users. Hence, anonymity is a useful tool for privacy and provides user’s anonymity. So far, several protocols have been designed to provide anonymity but most of the times, attackers found a way to take advantage of weaknesses in the design and implementation of these protocols. There is a class of attacks,where attacker tries to relate clients of anonymity system to each other, regardless of the communication protocols they use, just by observing networks traffic.The MIX technique forms the basis of many popular ervices that offer anonymity of communication in open and shared networks... 

In this study, static softening kinetics and microstructural evolution during isothermal and non-isothermal annealing of aluminum-magnesium alloy and low carbon steel after cold plastic deformation was investigated. It is known that in industrial cold forming processes, the material properties and microstructure changes during the annealing depends on the inhomogeneous initial microstructure and the deformation history of the cold worked material. To predict the microstructural changes during the annealing of cold worked alloys, a multiscale model based on probabilistic cellular automata (at mesoscale), and the finite element method (at macroscale), was used. To do so, a two-dimensional... 

Microfluidics is a field of science that studies micron-scale characteristics of fluids. In this scale fluids show fascinating behavior far beyond our expectation compared to their large-scale counterparts. One of such peculiar behavior is the mixing of two different liquids flowing inside a microchannel. Due to low Reynolds number, the flow inside such a channel would be dominated by laminar behavior. In this regime mixing of the fluids is only mediated by molecular diffusion which is a rather slow process. In the current thesis, we utilized the rotating ability of optical tweezers to construct an active micromixer for Microfluidics. In order to do this we used birefringent microbeads. The... 

Surface tension is the most important interfacial parameter of a liquid. This quantity plays a key role in many processes such as extraction, distillation, absorption and chemical reactions. Various methods are proposed for measuring this quantity among which, the laser based methods are the most accurate ones. Unlike most of the mechanical methods, laser based methods remotely measure the surface tension. The aim of the current thesis is to measure the surface tension using laser beam, more specifically using homodyne detection system. This method implemented in both reflected and transmitted modes. In each of the mentioned methods, first the laser beam was incident to the liquid-air... 

Intensity or phase Modulation of a wavefront is possible by means of optical devices. Placing a grating or lens on the way of a wavefront, will alter the phase or intensity of it and this will make a diffraction pattern. Spatial Light Modulator (SLM) is an optical device which is the most important part of a video projector. One can apply grating, lens and other phases on the wavefront using this device.In this project we used SLM to modify phase of laser beam and then we made many focal points such that they could displace independently. The result of this project can be used in designing and creating a holographic optical tweezers.Moreover, A. Einstein proved that the light could be... 

In past few centuries , dams have been always a crucial part of human life . Using dams for agriculture and supplying water for people , has made them a valuable asset for countries . So evaluating dam safety and dam breach properties is so important. This issue is a geotechnical , structural and hydrological matter. Safety of earth dams could be threatened due to dam body breach caused by overtopping or pipping, during heavy floods, strong ground motions or any structural damage or defection. As in previous studies , calculating the final geometrical breach properties and time of failure was the main goal , we tried to connect this characteristics and find the relation of time and breach... 

Viscoelastic properties of biological fluid play an important role on biological organs. As an example we all know that Red blood cells must have high flexibility to pass thorough thin capillary.This high flexibility come partially from cytoplasm and 2 dimensional membrane and partially from polymeric fluid inside the cell(hemoglobin). So, for recognizing mechanical properties of a whole cell we also need to study the same properties just for fluid inside the cell. for this general purpose through this project we are going to measure viscoelastic properties of any polymeric fluid by optical tweezers which has an ability for measuring displacement of micron particle with accuracy of nm. first...