Sharif Digital Repository

In this thesis, the optical force acting on the spherical polystyrene particle trapped by optical tweezers is calculated. The calculation is based on the generalized Lorenz-Mie theory. The effect of various parameters on the optical force is also investigated. It is shown that, tuning the different parameters, one can significantly enhance the optical force acting on the trapped particle. Besides, one can achieve a stable 3D trap of a sub-micron particle somewhere far deep inside the sample chamber. Our results indicate that: (1) By obstructing the central region of the incident Gaussian laser beam at the back focal plane of the objective lens, the trap stiffness, the maximum linear force,... 

Optical tweezers consist of a tightly focused laser beam. Particle with refractive index grater than that of the surrounding medium are eligible for optical trapping. This device is used for measuring forces from pico-newton to nano-newton, and displacements from nanometer to micrometer. In biopolymers, for example, it is used for studying the elasticity of DNA molecules, mechanical properties of cell membrane; and also in Microfluidics, it can is used for mixing two liquids flowing in a micro-channel by rotating a trapped particle. In general, physics of optical tweezers (or interaction of the trapped particle with the tightly focused laser beam) is treated in three different regimes:1)... 

As a new technology, the use of Solid State Disk (SSD) in storage systems is increasing due to its higher performance and lower power consumption as compared to the traditional Hard Disk Drive (HDD). On the contrary, the SSD technology has two serious shortcomings, i.e., 1) it has a higher Bit Error Rate (BER) as the number of Program/Erase (P/E) cycles increases, and 2) it can endure a specific number of P/E cycles, called the write endurance limitation. To overcome the endurance limitation of SSDs, several solutions have been proposed in previous literature. These solutions can be categorized in two levels: 1) SSD-controller, and 2) RAID–Controller. Moreover, it is necessary to consider... 

costs of construction of a structure include: initial construction cost, maintanance cost, seismic risk cost and etc., that in this investigation,the seismic risk of multi-span conc. & steel bridges has been compared. the seismic damage is converted to equivalent finincial value by the concept of life-cycle cost, and then is compared with initial construction cost of structure.in this method, assessment of seismic damage based on structure response, in different earthquake intensity and by damage state concept is done. ET method has been used for predicting response of models.in this investigation two conc. & steel models, with similar geometrical specification and different design results,... 

Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's...