Sharif Digital Repository

Nowadays, with the increasing need of various industries and applications to directly create linear motion, linear resolvers are attracting more attention than ever. Achieving high accuracy as well as measuring absolute position leads to the introduction of a new generation of resolvers, called multi-turn resolvers. Usually, a multi-turn resolver consisted of two individual resolvers in one frame, while using a common core for both resolvers can help to make the multi-turn sensor smaller, cheaper, and lighter. Nevertheless, the studies conducted on linear and multi-turn resolvers are very limited. Therefore, this research proposes an integrated core linear variable reluctance multi-turn... 

Temperature reduction from room temperature to liquid nitrogen temperature has a significant effect in improvement of semiconductor devices operation such as field effect transistors. Nowadays cryoelectronics as a considerable branch of electronics is concerned by several groups. In order to optimize the procedure of low temperature IC design and fabrication we investigated the temperature effects on different parameters of MOSFET in this thesis. Several transistors in a variety of channel lengths were fabricated in different technology files. Wide measurement experiments were done on these transistors in order to find their drain current vs. drain to source voltage characteristics. From... 

The aim of the current project is preparation, characterization and microfiltration evaluation of nanofiberous membrane. In order to prepare membranes, the electrospinning method was utilized and polyacrylonitrile and N-N, dimethylformamide (DMF) were used as the polymer and the solvent, respectively. As the nanofiber diameter controls the structure of the membrane and also bead formation reduces the membrane uniformity, at first the effects of four most influential electrospinning parameters, such as solution concentration, applied voltage, floe rate, and the distance between needle tip and the collector, on average fiber diameter and bead area density were investigated via response surface... 

Optical Tweezers (OT) are non-invasive micro-manipulation tools based on a tightly focused Gaussian laser beam for applying and measuring pico-Newton range optical forces. They are also utilized for trapping and moving particles and biological specimens. The force exerted by OT is mainly determined by detecting the position of the trapped object inside the harmonic potential well of OT. Conventionally,a Quadrant Photo-Diode (QPD) positioned at the Back Focal Plane (BFP) of the condenser lens provides the position of the bead with MHz temporal and nanometer spatial resolution. As a disadvantage of this detection scheme, it is impossible to obtain simultaneously the maximal lateral and axial... 

In this research, wear behaviors of 6061Al and 6061Al-20 vol% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 25- 200°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.34 m/s, an applied load of 20 N and 50N, and a sliding distance of 2450m using a pin-on-disc machine test. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects on wear rate of composite. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. Also for determining the effect of age hardening treatment on wear behavior of composite, specimens were solution treated at... 

Red blood cells (RBC, erythrocytes) are cells with an average diameter of 8 microns, the thickness of 2-3 microns and the volume of 90 fl. The biconcave shape of red blood cells,together with cell membrane flexibility, enables them to pass the capillaries whose diameter is considerably less than 8 micrometers. Mechanical properties of RBC are related to their membrane and cytoskeleton, which consists of spectrin network. Optical tweezers is able to exert very precise forces to erythrocytes using beed as a handle. In this report, we studied mechanical properties of RBC such as elasticity and viscoelasticity using single trap optical tweezers with beads with antibody coated in order to attach... 

In this project, Dissimilar Friction Stir Welding (FSW) between aluminum alloys (1100-H12 and 5083-O) and Magnesium alloy (AZ31B-O) with 3mm thickness were butt joined. Fusion welding of aluminum/magnesium alloys has failed because of forming much more intermetallic compounds. By using friction stir welded samples, effect of welding parameters such as tool travel speed, tool rotation rate, tool position respect to weld centerline, and sheet position respect to tool direction on mechanical (tensile strength, yield strength and elongation) and microstructural properties of the welds were investigated. After several tests, range of optimum parameters were obtained. In both 1100 and 5083 alloys,... 

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...